Who's using social networks?

My intrigue in social networks is recent. I've spent the past few months trying to gain a better understanding of who is using them and why. Admittedly I'm not big on social networks. I have a Facebook page that I never update and I'm on Linked In, which I tend to update only after receiving an invitation to join a colleague's network. I don't see a lot of value in the premise of having hundreds of "friends" whom I don't know, but happened to come by their email address at one time or another. It's akin to building a permission based marketing database. Yes, someone has agreed to hear from me, but that doesn't necessarily mean they're hoping I take them up on the offer. The other reason I don't see a lot of value in social networking is because the majority of my friends aren't there, and most don't have a desire to participate in the space. It makes me wonder if my set of friends is so unique to be immune to what is purportedly exploding all around us or if the use of social networks is being over-projected to a larger demographic than the active user base. When I ask people why they don't use social networking sites, twitter, blog, etc. (and we go through the explanations of what I'm talking about) it becomes apparent - my friends, much like myself, are too busy to maintain the effort. Between careers, family and a social life there isn't a lot of time left to participate in an on-line life. From there I think about the people that I know that do use the technology and it always comes down to two major categories - marketers (who are there to figure out why other people are there and to figure out a way to capitalize on that) and the people in their mid-20s that I met while in my graduate degree program. What will be interesting to follow is if the people that were active Facebook users while going to school (and not working) continue to be as active once they graduate and land full-time jobs. It's at that point that the real value of social networking may become clearer.