1) Because it allows me to stalk people I haven't seen/heard about in 15 years and see what they're up to, who they married, if they have kids, where they've traveled, etc.
2) Because with that information I can fall back into high school mode of "Oh my gosh did you see what so-and-so is doing now and that she married whozit and can you believe so-and-so has 14 kids??" about people that I didn't know anything about 3 days ago, but now am consumed with whatever they're doing. For like 1/2 an hour anyway. And then I let it go.
3) Because it is really nice, all things aside, to be able to put an answer to the question "I wonder what happened to...?"
Having gone to a small, all-girls Catholic school, our graduating class was under 150 girls. I think that at least half of us are on Facebook. And I find it so nice to see what everyone is up to. We had a close-knit class, and a lot of people stayed local, and so a lot of people you still run into here and there, at Fests and such, you know, like you do, and you can usually find out about everyone else through the folks you run into.
But people that moved away? People that were total wallflowers? I love seeing girls that barely spoke a word (Or at least not to me, I may well have been a total b*tch to people without realizing it back then and so people didn't want to talk to me. (Nowadays I fully realize that I am a b*tch.)) in high school who have become amazing women, funny and speaking their mind and with amazing careers and families and lives.
And I love it!
But mostly I'm in it for the legal stalking.