Concentrate on one?

Is it better to be involved in every kind of social networking things that's out there, or to concentrate on the top three/five/whatever? I've never even heard of some of the newer social networking sites out there, and I wonder if it's even worth trying to do anything with them until/if they get more popular.

Follow wherever your target audience is or might be. All press is good press. Just think of it as free advertising (which it essentially is).