Arguably, this fulfils a valuable social function. The confident are there, as they would be wherever an audience gathers to applaud their talents. But so are the wall-flowers and the misfits, receiving a share of attention they wouldn't get from conventional social interactions.

Saying who you are, what you're thinking, what you're feeling is a lot less scary when you're telling a computer screen than the wide-eyed faces of intimacy-phobic mates.

Michael Birch, the 36-year old San Francisco-based British founder of Bebo, argues that social sites help young people to learn how to communicate and develop multi-media publishing skills.

But teens are notoriously fickle: fashions, friends, music and fads rise and fall with alarming velocity. Will social sites last?

"Bebo is bitchier than a school playground," says Beth, 18, already disillusioned with the scene. "It's full of boys trying to be cool and tweenies posing in their underwear and lipstick."

Sites that accrue a wide demographic are less vulnerable to the capricious cool factor. Older people are increasingly frequenting social sites. About 36 per cent of MySpace users are aged 35-54, according to comScore Media Metrix.

One group which hopes that social sites will continue to flourish is the advertisers, attracted to huge, potentially lucrative, young audiences. If there's a predictable future for the big social networking sites, it is as a marketing vehicle.

So-called youth brands such as Sony, Coca-Cola and Apple have found success promoting their wares on social sites and not just through conventional advertising.

Apple sponsors a Mac-help group on Facebook, which was established independently by US college students.

Kids don't buy stuff because they see an ad. They buy things their coolest peers have got. What better way to find out what's hot and what's not than checking out the cool people's likes and dislikes lists?

This is similar to the 'influencers' used by record labels and brands such as Nike in the early 1990s.

Influencers in their late teens and early 20s were, and still are, paid largish sums of money to sample their peer-group zeitgeist and talk up the wares of their paymasters.

Using social networking marketing is seen as a brave move to make a brand relevant to young people. Well, that's how marketers present it. But it could also be interpreted as another example of the commercialisation of youth,

Advertisers hijack new trends so they can peddle their wares to the young and gullible, in much the same way that popular music, video games, skateboarding, graffiti and many other 'youth activities' are subverted to serve the dark legions of the corporation.

But restless young people will find ways to avoid the marketing machine as it chases them relentlessly from one cool thing to the next.

There's probably at least one 15 year-old 'nu-goth' expressing that opinion on MySpace right now, before he sets up his own rival site.