Facebook: it has done for HSBC, Cadbury and even Sky Sports. The social networking website, which has gone from nothing to a company worth an estimated $5bn in the blink of an eye, is being heralded as the great new way for consumers to get even with their banks and apply pressure on errant corporations.

Already it has 30 million users worldwide, five million of them in Britain, and is adding 200,000 a day.

Compare this to the one million members of Which?, the consumer group that celebrates its 50th anniversary this year, and it clearly isn't hyperbole to describe Facebook as a phenomenon. But has it really ushered in a new age of consumer activism?

As well as allowing people to lead online social lives, the website gives users carte blanche to vent their frustrations about corpo- rations within a community of millions. The theory goes that if you and a friend have a gripe about Tesco, say, then there is little you can do about it. But if you and 10,000 others on Facebook share that gripe, you can become a consumer force.

Anyone still sceptical about the power of Facebook should speak to executives at one of the world's biggest banks. Last month, HSBC was forced into a humiliating climbdown over its decision to end the interest-free overdraft facility on some of its student current accounts. This followed a campaign on Facebook mounted by thousands of outraged students – a story that hit the headlines. After trying to hold its position, the bank caved in, issuing a statement that it was "not too big to listen to the needs of customers".

But the widespread theory that it was "Facebook wot won it" should, it seems, be qualified.

The campaign was co-ordinated by the National Union of Students, and when HSBC climbed down, it did so following discussions with the NUS. So any idea that the initiative simply bubbled up in cyber- space should be dismissed. Facebook made it more efficient but this was princi- pally a success for unionism.

Martin Lewis, who runs the consumer website Moneysavingexpert.com, says the campaign was "lucky" and he was shocked when HSBC backed down."

"It [Facebook] might be bringing new ways of organising consumer action, but it's more a minor evolution than a revolution."

This is a view shared by longer-established custodians of consumer rights. Which?, for example, does not see Facebook as a threat but is looking instead to harness it. "The site's popularity can be used to gather consumer support," says a spokeswoman "It is something we'd consider using in the future to mobilise support from consumers."

A quick trawl through Facebook reveals a rather idiosyncratic activism – people trotting out their own hobby horses in the hope that other users will leap on. These campaigns are about outing big and small companies alike for individual instances of poor service; they are not the next HSBC. Even some of the high-profile Facebook successes – getting Cadbury to start selling Wispa chocolate bars again or Sky Sports to change the way it displays the scores on live football matches – are hardly big issues

Without leadership from outside, argues Mr Lewis, Facebook is something of a blunt weapon in promoting the interests of consumers.

"It is very rarely the little guy sitting in his garage. Usually he has to contact someone in an organisation or the media," he explains. "If you look at the big campaigns, most of them have some form of leadership through an official organisation."