Every one of them sent Friend requests to me, not the other way around. Some of them I had a few classes with and talked to, but didn't exactly hang out with, and some I knew through other people. I was a loser in high school and still am today, so I'm always surprised, but hey if some chick wants to be my Facebook friend, I'm okay with that.
And really, they're just virtual friends, and I treat them the same as any other. Post funny comments once in a while, answer questions, that kind of thing. It's not any different than what we do here on message boards, except it's all people I know in real life. I never asked them to post bikini pictures of their trip to Orlando or Cancun for me to check out, but since they do, I feel like I have to oblige. It's only polite.