The beginning of the end for the social networks?
Are we seeing the beginning of the end for Facebook and the like? It's hard to believe, as they're still growing by leaps and bounds.
But people are fickle, and it's happened before. Some of the earlier social networks (Friendster and MySpace come to mind) have stagnated and are not cool any more.
Facebook and Twitter have both had problems recently: Facebook's redesign and the kerfuffle over it's terms of service; Twitter's ongoing reliability problems and, just yesterday, a virus (technically a worm).
These sorts of problems are probably inevitable. When a site depends on its users to create content, there are going to be users who will misuse their authoring capabilities to spread spam or malware, for financial reasons, or just to show off their technical prowess.
And the social networks do compete with each other. There are over a hundred of them now, but no one has the time or desire to participate in all of them, so each network will try to come up with features to attract users to their site, rather than someone else's. In fact, many sites have figured out ways to import content from, and export content to, other networks.
This situation is a natural outgrowth of the preferences we've been taught in older media. We're used to advertising-supported modes of entertainment. The subscription model hasn't worked on the web, and isn't likely to.
So we've brought together user-generated content, advertising support, and a boom mentality where technical controls are minimal. The perfect conditions for the coming together of Murphy's Law and Sturgeon's Law ("90% of everything is crap").
As I see it, it's not evident that social networks will go the way of the pet rock. But it seems to me that a lot of sites will disappear, and only the strongest will survive. It will be interesting to see who makes it to 2010.

Once a site or network becomes too crowded or popular, it will become un-cool, and the cool people (by that I mean, the people other people model their behavior on) will move someplace else.
Sites like Linkedin might survive (it seems by far the longest lasting of the social networks, if you don't count the 'net itself) because it actually provides a service.
It'll be interesting to watch. I do chuckle whenever I'm reminded that Murdoch spent billions for MySpace.