LinkedIn recently suggested my neighbor from 1995. I didn't even have Internet access, let alone an email address back then. I haven't had any contact with this person since.
That or they have information on where you and your neighbor once lived. I have signed up for a couple of online brokerage accounts where they ask me questions about where I or my family have lived in the past.
I got questions like; "At which of these 5 addresses has $BROTHER ever lived before?" And one of them was correct.
Why would it be creepy for someone using a social networking site to search for people they've met over the years?
Also, how much of the perceived "creepiness" of someone searching for someone on LinkedIn just a variation of this: http://thedoghousediaries.com/1042 ?