Yea sites like these are definitely creepy in the sense that you don't always know who is out there.
I use myspace, facebook, etc. but I only "friend" people that I have actually known longer than 5 minutes. I may not have 355426863 people on my friends page, but I know who they are
When thefacebook.com first got launched, I didn't find it until after I had graduated. I thought the idea was really neat in the way that you could search and find people in your classes andmeet people that way, but it also freaked me out that my entire school schedule would be online for all of the world to see which is disturbing in a way.