Exactly. Facebook has worked so well in part because it forces people to be less anonymous. You are prompted to use your real name and put in factual data about yourself, and when you becomes friends with other people it connects you via all of their other tools. So yes, you could become friends with people from high school you don't know, but your pictures will be with your actual friends, which really is showing that, in private, you hang out with certain people.
I don't see how a factual representation of the self is necessarily bad, though. Yes yes, there's the whole "if you're not breaking the law, why are you afraid of the law" argument, but Facebook does let you lock down your profile pretty well nowadays. The latest privacy hubbub is about how Facebook is linking into other sites like CNN.
MySpace was always a bad model for social networking as it was little more than GeoCities templates with a friend feature. Facebook is actually social networking. But like IM protocols, how many do you need? Sure there's going to be some people who really care about anonymity and prefer something like Diaspora (or ICQ). But the idea of " social network" and privacy/anonymity seems kind of at odds, doesn't it?