A lot of comment on various blogs and news sites recently speculates about why social networks have taken off so spectacularly, and where they might be headed - too many sources to mention each individually, but a particularly good overview to the background is an article on AlwaysOn, The IM Generation in Charge, and the UK's Observer Review's analysis of some of the most popular sites, and the way young people are using them.

One of the IM Generation's main points is that the idea is not fundamentally new - it's not radically different from the way early (pre-Web) Internet users forged communities to connect themselves using bulletin boards, but it's got the power and immediacy that IMers demand, allowing them to be creative, show off and share with people they mostly already know - so more about increasing the variety and quantity than the range of communication.

What the Observer article focuses on is how people actually use the big social networks, looking particularly at Bebo, whose founder Michael Birch started the site for people like himself - 30-somethings - and found it taken over by teenagers, who had more time on their hands and liked being able to keep in touch with each other for free. The article also makes a distinction between social network sites used predominantly by young people, which are mostly about self-expression more than to increase their social circle, and older people who want to deliberately build networks for particular purposes, a pattern that relates much more closely to social network theory.

To me it makes sense to ask whether there are fundamental rather than surface details that differentiate networks that appeal to different age groups. I meet quite a lot of teenagers, and on that limited basis the answer is almost certainly "yes". It seems to me that most teenagers work out they are and what interests them through intensive contact with their peer group, and gradually gain the confidence, knowledge and versatility they need to adopt the more extensive approach to socializing demanded by moving away from parents, trying to find a suitable partner, building useful business relationships and getting help with life problems.

For young users, then, who are the driving force behind the popularity of social network sites, it makes sense that they know most of the people they interact with other anyway. The web means building on the type of things they already like doing, while exploring in a trusted and controllable space, where they feel able to speak and do as they please. That trust is likely to be less a matter of security in a more general sense or of freedom from commercialization than freedom from interference from authority figures or people who remind them of their parents. MySpace has obviously got this right (for now at least). Names are also obviously extremely important in this way. MySpace, Bebo, and YouTube all manage to be memorable but at the same time low-key and personal.

Demographics - i.e. the core customer base ageing - probably means that sites' offerings will differentiate and develop over time and lose their appeal to younger web users. At the same time they will lose many older users who will "grow out of" the content, lose interest or object to commercial content or problems with the brand. My guess is this will likely mean major players letting old sites go to pasture and acquiring new brands every few years. So after a consolidation phase as the youth market saturates and new users find a site they trust and that does all they need, new brands will emerge - perhaps every year or two, much like trends in popular music, while the leavers migrate to some of the other business-related networks offering more extensive networking opportunities, or join more selective special interest networks to meet like minds.

On that view of the youth market, I think an important step will be making the social space feel more real and immediate. The outside world in many places is just not interesting for young people, as good recreational spaces are often scarce, expensive or age-restricted. What I suspect many would like is to watch, listen or play games together while chatting, which they can already do, but with the added ability to see each other in real time, perhaps even incorporated into other content, so they also gain the immediacy of non-verbal communication.