I really like facebook, but I have a good friend who just can't deal with it. It really does help me stay connected to some people who have drifted a little. I'm older than a lot of y'all (49 now!), and have friends who are the same age, but didn't have kids. We drifted apart when I had kids and got connected with the mom groups. It's nice to reconnect with those folks. There are some folks from high school and my hometown that I am not really close with and a few folks that I have hidden (relatives on DHs side mainly) and I do sometimes control who can see what I post (not acquaintances, only close friends). I have a fairly large number of friends, though, and I think that's what makes it work for me. I am fb friends with a lot of people from throughout the different stages of my life. My friend who couldn't hang with fb had a small number of friends and was getting friend requests from people she went to high school with and didn't want to stay in contact with. She didn't want to share pix of her kid or tell them what she was up to. When you have a large group of fb friends it's more like a community newspaper or community-wide gathering than a dinner party.
We're facebook friends with a lot of DH's college friends and it's such a great way to stay in touch with them. They and their spouses and families are a great group we really love, but they're very far flung (Seattle, New York, PA, KS, sometimes Europe, etc). We used to have New Year's Eve party every year before we had families and they would come from all over. It's like a mini-reunion on fb all the time. I have good friends in LA from my brief sojourn there and I'm able to stay in touch and see their kid growing up.
I think the key for me is to really manage my friends. I hide the ones I don't want to see (have a couple who like to post about their selling businesses — thirty-one, etc; and one or two who like to post about their bunions, etc) and control who gets to see what I post and I have enough other friends and other likes (causes, pages, bands, authors) that I get to see something I am interested in instead. My friend who only had 35 or so friends was only seeing status updates from people she wasn't that interested in.
I'm also fairly self-conscious and don't update my status a whole lot. I'm more likely to "share" an interesting tidbit (shared about the chromatic typewriter today, which is really cool) or to comment on someone else's status. I do really like social media for its organizing abilities. I've gotten involved in some political protests about issues I really care about because I saw it on fb. My friend without fb also cares about these issues, but she didn't know about the protests.