If I opened it up to everyone I know from high school and college that I've found on facebook, I would easily be in the hundreds. But then it would be "aquaintancebook" not facebook.

I have 4 teenage relatives on my friends list. I try not to embarrass them, but I do pay attention to what they're up to just to keep an eye on them. They all have other adult relatives on their friends lists, which I imagine is required by their parents.