It's interesting to think back to 2007 and the 23 ½ things at Queens Library which introduced me to some social media sites. I hadn't used Facebook before then, but it's become an important way for me to stay in contact with friends, family, and colleagues. I've used it in ways would never have expected (like meeting a friend for lunch when at a conference by just saying "is anyone near this corner and would like to meet for lunch?). It's fun to share photos and experiences. Of course, social media is also in some ways like having a diary--but knowing that it's going to be read every day by people you know and people you don't know. So, I share what I think will be interesting to my "friends" that I also wouldn't mind being read aloud at work.
Facebook is pretty much my social media "home". I say to much for Twitter and there's a little too much arguing there (at least among people I know). I don't take enough pictures for Flickr. I do keep a profile on LinkedIn, especially for conference speaking opportunities.