Know what I want? An antisocial network.
Every time I end up joining another one of these services, I go through the same frustrating process of adding all the people that I "knew" on previous social networks to the new one. I find this both exhausting, and, to some extent, embarrassing, since I don't actually have that many friends. And I kind of like it that way, honestly. I'm not really the kind of person who goes out of their way to contact other people unless I've actually got a good reason to do so (although I do feel bad about my terrible blog commenting habits lately, and have resolved to do better). I'm not trying to reach some kind of social network "high score," in other words--not that there's anything wrong with that.
The sensible way to fix social networking transfers, in my opinion, would be to have a common interchange format--JSON or XML--that you could download from one service and upload to the next. Combined with something like OpenID, we could skip the entire hassle of starting from scratch on a new network. Facebook and Twitter, at least, have not done this. Instead, they've put together some kind of creepy API-based address book import, where all you have to do is give them your e-mail password. This is both terrifying and idiotic.
You could argue that social networks want it to be hard to move between them, because then they're less likely to lose subscribers when new contenders show up. But I'm not sure this is actually a concern. I think most people would be more than willing to belong to more than one competent (read: not MySpace) social network, if for no other reason than it gives them more stuff to obsess over during their workday.
So sometimes, when I'm idly trying to figure out how to motivate myself to use these services, I think about my antisocial network. I'm hip-deep in Flash at work, so I can't bring myself to look at Actionscript in my spare time, but once I get free I think it might make a good Facebook app: a social network where you can't friend anyone, and instead of poking and verbing people they can only be shunned (an action which sends the target no notification at all of their status). I imagine a network topology as a globe filled with dots, each a node in the web but with no lines connecting them, like a constellation of potential friends forever just slightly out of reach.