Definitely depends what kind of situation you're in. Facebook for example was at first only allowed for college kids. It only recently broadened to kids in highschool, and then to everyone. On a college campus, facebook is ideal for finding out about events, speaking with classmates you don't know well, and keeping in touch with friends in general. If I wasn't in college, probably wouldn't even have a FB account. I see that myspace is mostly used nowadays by musicians and models, which must be it's ideal use.