I just signed up for Facebook and I haven't had any highschool people I don't know contact me. BUT I have had a TON of scrapbooking people I don't know want to be friends with me!
It's kinda funny. I always accept because I don't really care. I was SUPER shy in highschool, so most people probably still don't know that I even exist! I have gotten in touch with some of my very best friends that I lost touch with in college. That is really cool. I think that a lot of people are just looking to network. They don't necessarily want to be your best friend, just keep options open. They may know someone who could help you out sometime.