Love her or loathe her, it's impossible to ignore Joan Rivers. Few opinions are going to be changed by Ricki Stern and Anne Sundberg's up close and personal profile, Joan Rivers: A Piece of Work. But this isn't a celebration of a trail-blazing and often contentious career. It's an insight into the difficulty of staying at the top in the amnesiac world of show business and how willing Rivers is to do just about anything in order to feed her work addiction.

Despite becoming Johnny Carson's favourite guest on The Tonight Show, Rivers never forgot her ambition to become an actress and her failure to convince the critics of her dramatic worth is one of the many poignant revelations in this riveting year-in-the-life snapshot. Indeed, she suffers more slings and arrows after the autobiographical play that had triumphed in Edinburgh receives lukewarm notices in London and all hopes of a Broadway opening disappear with the smug invective of the British press. Consequently, Rivers is forced to return Stateside to resume her punishing schedule of club dates, shopping channel sessions, radio interviews, book signings and personal appearances. She is also slated to appear alongside her daughter Melissa on Donald Trump's Celebrity Apprentice and hopes that a decent run will land her higher profile gigs than a Comedy Central roast and a memorial for George Carlin.

But staying in the limelight is just one of Rivers's problems. She also has to deal with her ultra-competitive relationship with Melissa and the fact that manager William Sammeth is becoming increasing unreliable and that she risks losing one of her few remaining confidantes if she fires him. This dislike of feeling alone goes some way to explaining Rivers's workaholism. But there's also a sense that entertaining her fans and disproving her detractors gives her a reason for living. Moreover, performing also allows her to entitled to the luxurious Fifth Avenue apartment that she claims Marie Antoinette would have copied if she'd had the money.

At 75, Rivers is renowned as much for her plastic surgery as her comedy. Yet she frequently allows herself to be seen without make-up here, as though to reinforce the honesty of the portrait and the sincerity of the pain when she recalls the sense of betrayal she felt when husband and manager Edgar Rosenberg committed suicide following the fiasco of the Fox chat show that cost her Carson's protective patronage. But this isn't all about struggle and introspection. Archive clips are juxtaposed with routines from Rivers's typically caustic stage shows, with one encounter with a Wisconsin heckler who takes exception to a deaf joke exposing the yen for acceptance that underpins her fast-talking, expletive-strewn, self-deprecatory schtick.

If Stern and Sundberg adopt a globe-trotting approach, Chris Smith prefers intimacy for Collapse, which affords a platform for the strongly held and trenchantly expressed opinions of Michael Ruppert, a former LAPD officer who has spent the past three decades disbelieving headline news stories. Both a compelling study of a man on a mission and a terrifying warning about the global ramifications of an oil crisis, this talking-head documentary audaciously allows hard-hitting fact and more specious supposition to compete for the viewer's credulity.

Having come to wider attention in the 1980s after accusing the CIA of involvement in the drug trade, Ruppert became a crusading journalist for his own newsletter, From the Wilderness. A scathing critic of the Bush administration, Ruppert predicted the credit crunch and he is now convinced that a greater catastrophe is inevitable unless humanity changes its mindset. Insisting that market capitalism's trust in infinite growth is a reckless folly based on a lie, he makes his case with a persuasive mix of cogency, passion and gallows humour and not even the odd lapse into hyperbole and contradiction can discredit his plausibly apocalyptic vision of a future without fossil fuel.

Resident in Culver City in California, the chain-smoking Ruppert devotes himself to his dogs and wondering where the next rent payment is going to come from. Yet he has not abandoned his bid to persuade the public to lobby their elected representatives and bring about reform before it is too late. However, in addition to promoting political iconoclasm and such eco theories as self-sufficiency in food, Ruppert is also a firm believer in 9/11 conspiracies and it's telling that Smith elects not to raise this issue on camera, as he allows cinematographers Ed Lachman and Max Malkin to perform elaborate manoeuvres on Andrew Reznik's stark set in order to evoke the style of Errol Morris's The Fog of War (2003). But, if he overdoes this interrogatory gambit, Smith makes able use of archive footage and creates the relaxed environment that allows Ruppert to hold court with an informed fury and candour that makes this tough, but necessary viewing.

If Smith occasionally raises a quizzical eyebrow at some of Ruppert's ideas, David Bond takes himself deadly seriously in Erasing David. But this exposé of surveillance Britain is little more than a shameless exercise in cynical self-promotion, which is made all the more egregious by the fact that it was conducted while Bond's wife was about to give birth to their second child.

Having learned that his daughter Ivy was one of the 25 million UK residents whose details had been lost by the Child Benefit Office, Bond decided that the best way to reclaim his privacy was to see how easy it would be to disappear off the radar and remain hidden for a month. To make the challenge more interesting, he contracted a couple of private investigators to see how long it would take for them to track him down. As Bond traversed the country, laying low and sleeping rough, the bloodhounds trawled the internet, as well as rummaging through bin bags and snooping on known acquaintances, in order to pick up the trail. Yet he is finally caught out attending an ante-natal check up at his local hospital.

In fairness, Bond raises some disconcerting issues about identity theft, the nonchalance with which institutions share information and the ease with which the government has been able to erode our civil liberties in recent years. He also gleans useful insights from experts like clinical psychologist Daniel Freeman, as well as those who have suffered from online scams, identity fraud and DNA bungles. But his structuring of the footage is clumsy in the extreme, while Bond's pieces to camera have a smugness that sits uncomfortably with the ungainly naturalism of his pursuers.

Dylan Goch makes a much better job of capturing the quirky personality of Super Furry Animals frontman Gruff Rhys, as he ventures into Patagonia to track down distant cousin René Griffiths in Separado! Having been transfixed by the singing gaucho's appearances on Welsh television in the 1970s, Rhys is keen to discover the extent to which Cambrian culture continues to thrive in the Argentinian backwoods. However, the elusiveness of his quarry forces Rhys to undertake the quirkiest promotional tour of his entire career.

Opening with a stylised flashback to a fatal horse race in Bala in 1882, this determinedly low-budget documentary threatens immediately to go off the rails with a bizarre musical number about Welsh emigration in the 19th century. Rhys's habit of periodically donning a Power Ranger helmet to teleport himself across time and space proves similarly off putting. But such eccentricities end up adding to the offbeat charm of this highly personal picture and it even becomes possible to overlook the gratuitous overuse of split-screen sequences.

After various relatives and historians have filled in the socio-economic reasons for the founding of a Welsh outpost on the Chubut River in 1865, Rhys crosses the Atlantic to follow the fortunes of his ancestor, Dafydd Jones. Having detoured to a seemingly lost Celtic settlement in Brazil, Rhys makes contact with Griffiths's kin and hits the road with cousin Cecilia as his guide. They pass through communities like Gaiman, Dolovan and Trelew, whose links with the homeland are evident in their Bethel chapels and tea rooms. En route, Rhys does radio interviews, jams with local musicians like Osian Hughes and Tony Da Gattora (who has invented his own guitar-style percussion instrument) and plays gigs for often bemused audiences, who are just pleased to have a celebrity in their midst. But there's no sign of Griffiths.

Ultimately, this is little more than a glorified home movie. But Rhys proves an engaging travelling companion and his generosity towards fellow musicians like crooning siblings Leonardo and Alejandro Jones is touchingly genuine. The structuring and technique are undeniably haphazard, but this remains a pleasingly idiosyncratic variation on the Who Do You Think You Are? format.

Back in the real world, a stark snapshot of combat is provided by Sebastian Junger and Tim Hetherington in Restrepo. Filmed over 15 months in the Korengal Valley of Afghanistan that was dubbed `the most dangerous place in the world' by CNN, this is a graphic insight into the near-impossibility of the Allied mission against the Taliban and the apolitical attitude of American troops who fight not for a cause, but for their own lives and those of their comrades in arms.

The focus falls on the Second Platoon, Battle Company of the 173rd Airborne Brigade as it arrives in Korengal in June 2007 under the command of Captain Dan Kearney. He is keen to win the hearts and minds of the locals, who not only endure countless friendly fire casualties, but also reprisals from an essentially invisible enemy. However, Kearney is also determined to erect an outpost on a key Taliban weapons route and he catches the counter-insurgents by surprise by dispatching a nocturnal detail to dig in while conducting frequent fire fights. The OP is named after Juan Restrepo, a 20 year-old medic who was the unit's first KIA, and the esteem with which he was held by his buddies makes them all the more intent on holding their position and making a difference in the war.

However, it soon becomes clear during Junger and Hetherington's subsequent visits that precious little progress is being made by the platoon and that as much time is being spent sitting around waiting for the next firearms exchange as it is building bridges with the dirt poor peasants whose weekly meetings with Kearney reveal only their growing suspicion of the Americans and their constant terror of the Taliban. However, the soldiers have little regard for the people they're supposed to be winning over. As they have such scant knowledge of the terrain, its inhabitants and their cultures, they treat everyone as a potential terrorist and dismiss claims for compensation for lost belongings with a high-handedness that betrays their indifference to the geo-political significance of their cause.

Indeed, it's only when they mount Operation Rock Avalanche, in a bid to root out the jihadists being succoured by the villagers, that they risk coming face to face with a foe they despise rather than respect. Consequently, when the death of a much-loved sergeant provokes a furious backlash, there's an almost triumphalist sense of vengeance when one trooper watches a target fall through his gunsight. It's warfare as computer game and it's only when brutality lands on their own doorstep that many of these young men recognise it as the hideous reality it is.

Respectively the author of The Perfect Storm and an experienced photojournalist, Junger and Hetherington succeed in capturing the nightmarish conditions experienced by civilians and combatants alike. Yet, by interspersing vérité footage with the talking-head recollections of veterans Kevin Rice, Brendan O'Byrne, Aron Hijar, Kyle Steiner, Misha Pemble-Belkin, Mark Patterson and Miguel Cortez, they have been criticised for lacking a coherent narrative. Yet the whole point of this uncompromising record is surely to expose the lack of a plan in Korengal and there's a chilling irony in the closing caption, which reveals that the outpost was abandoned with nothing tangible achieved.

Chen Suqin must harbour similar feelings of futility at the end of Fan Lixin's Last Train Home, as the global economic crisis forces her to abandon the factory job she has held for 16 years and return to her small farming community in Sichuan province. What makes her redundancy all the more affecting, however, is the fact that it comes after the domestic spat she had long feared would alienate her and husband Zhang Changhua from their rebellious daughter Qin and her younger brother, Yang.

Each year, some 130 million Chinese traverse the country to be with their families for the New Year festivities. For Chen and Zhang, this means travelling by train, boat and bus over 1200 miles from the industrial province of Guangdong. But Qin and Yang have seen so little of their parents since they were entrusted to their peasant grandmother that they scarcely have a word to say to them. Eventually, Qin announces that she is bored with living in the back of beyond and intends dropping out of school to work in a garment factory in Shenzhen.

Ignoring all lectures about the value of a good education, Qin embarks for the big city and makes the most of the long hours and the inconvenience of living in a crowded dormitory, as she now has the freedom to buy her own clothes and go to nightclubs. However, when she returns to Sichuan for the holidays, she has a blazing row with her father that not only ruins the occasion, but also seems likely to drive a permanent wedge between the increasingly independent teenager and parents who feel hurt by her lack of gratitude (after all the sacrifices they have made on her behalf) and regretfully guilty at having missed out on seeing their children grow up.

Adopting a vérité approach and ingeniously conveying distance through his use of cramped interiors, Fan avoids placing any blame. But it's clear from the chaotic transit sequences that the human toll taken by China's Economic Miracle has been immense. The second journey is particularly arduous, as snowfalls lead to the cancellation of services and thousands being stranded at remote stations. Having been harassed by soldiers, railroad officials and fellow passengers scrambling for seats on the next available train, it's perhaps unsurprising that Zhang's showdown with Qin should turn violent.

Tempers also come close to fraying in another study of getting by in a rapidly changing world, Marc Isaacs's All White in Barking. Questioning the notion that everyone prefers to live amongst their own people, this is a gently satirical, but occasionally dismaying film that suggests that there's a bit of multiculturalism in us all if only we're prepared to look.

Dave may be a BNP activist who would rather move to Canvey Island than see his estate lose its former character, but he's devoted to his mixed-race grandson, even though he gives daughter Charlie an earful for condemning the boy to a lifetime of prejudice. Nearby, Jeff and Susan are suspicious of their Nigerian and Albanian neighbours. Yet they end up inviting them to a barbecue after a night of African cuisine with Dickson and his wife Victoria waylays some of their misgivings. Only market butcher Steve remains unreconstructed, as he loses trade to interloping ethnic rivals. But his sour remarks pale beside those made during a Holocaust reunion, as a Polish charmer named Monty introduces his pals to his Ugandan companion, Betty.

Twinned with this unsettling snapshot of Essex folk in action is Men of the City, a study of working life that benefits from the documentarist's knack of being in the right place at the most opportune time. Initially, this was an investigation into the work ethic and the survival instinct, as Isaacs meets Steve, a street sweeper whose lonely, pre-dawn vigil has given him a spiritual insight into the daily grind; Fakhrul, a Bangladeshi single father, who has to juggle two jobs to support his young daughter; Andew, a metal broker with a passion for fox hunting; Norman, a chain-smoking insurance veteran who no longer has the stomach for the fight; and David, a stockbroker whose workaholism has cost him his family.

However, the tone changes dramatically, as the collapse of Lehman Brothers occurs while Isaacs is at David's desk and he records the expressions of disbelief and helplessness as the already stressed financier watches one of the world's biggest investment banks go to the wall. There is tangible drama in this unbearably tense sequence and while it isn't likely to persuade many viewers to pity a man on an annual salary they couldn't hope to earn in a month of Sundays, it provides some compelling insights into the speed with which events move and the difficulty of arresting a crash once it's started.

Isaacs presents another side of David, as he joins his family for a weekend at the seaside. He observes the pleasure he derives from playing with his kids and his passion for photography. Isaacs even coaxes a fulsome testimonial from David's ex-wife, who blames the long hours for the breakdown of their otherwise successful marriage. But Isaacs seriously misses his step in clumsily using the sounds of a hunt in full cry as an accompaniment to images of Andrew and his colleagues striving to make a killing.

Indeed, one would have to go back to the earliest sound documentaries to find an equally blatant audiovisual juxtaposition. Certainly film-makers of the calibre of Lindsay Anderson, John Krish, Jill Craigie and Derrick Knight would have avoided such a cheap shot, as the BFI demonstrates in its latest collection of classic actualities, Shadows of Progress: Documentary Film in Post-war Britain (1951-1977).

During the 1930s, the British Documentary Movement established the tradition of lyrical trenchancy that went on to inform the social realist style. However, a new generation of film-makers sought to shift the emphasis of actuality. Confronted with a rapidly changing socio-political scene and the demands of commercial sponsors, these documentarists exploited technological advances to produce films on a wide range of subjects that now provide an invaluable record of British life as the nation readjusted to its new place in the world. Indeed, far from witnessing a decline that was only arrested by the emergence of Free Cinema, the British documentary rose to the challenge of finding fresh ways of presenting information and promoting products, companies and social and charitable initiatives.

John Krish's The Elephant will Never Forget (1953), They Took Us to the Sea (1961) and I Think They Call Him John (1964) were discussed last week in the context of the theatrical compilation, A Day in the Life. But the remainder of this excellent selection is just as diverse, as it considers such aspects of British life as reconstruction, health, industrial relations, technological advance and ecology.

Perhaps the best-known title is Lindsay Anderson's Thursday's Children (1954), which was narrated by Richard Burton and reveals how the toddlers at the Royal School for the Deaf in Margate learn about speech. However, his 1952 short, Three Installations, and the 1955 pair, Henry and Foot and Mouth, are also included, along with Krish's Return to Life (1960). Also worth noting are Jill Craigie's To Be a Woman (1951), which tackles the topic of inequality in the years after women played such a key role in winning the war; Anthony Simmons's Sunday By the Sea (1953), a rousing day in Southend that won the Grand Prix at the Venice Film Festival; Guy Brenton's Four People (1962), which includes songs by folk legends Ewan MacColl and Peggy Seeger; and Eric Marquis's Tomorrow's Merseysiders (1974), which views the changing face of Liverpool through the eyes of journalists on its daily papers, the Post and the Echo.

There are also plenty of gems on offer in COI Collection: Volume 4 - Stop! Look! Listen!, a compendium of public information films made between 1949 and 1992, many of which still have an arresting power. The standout is Jeff Grant's Lonely Water (1973), which warns against the dangers of playing by deceptively deep rivers and pools and makes suitably sinister use of images of the Grim Reaper and Donald Pleasence's insistent voice. However, Sarah Erulkar's Never Go With Strangers (1971) and John Mackenzie's farmyard perils piece Apaches (1977) are equally striking, especially as the latter was made just three years before he directed The Long Good Friday.

Another high spot is Richard Massingham's typically droll 30 Miles an Hour (1949). But viewers of a slightly younger vintage will enjoy seeing Keith Chegwin showing off on a bicycle in Betcher! (1971), Valerie Singleton running through the Green Cross Code in Mind How You Go (1973), Frank Bough doling out motoring advice with a little help from future Doctor Who Colin Baker in Drive Carefully Darling (1975) and Gillian Taylforth learning the hard way about first love in 20 Times More Likely (1979).