I checked this once, and the amount of dangerous (ie, rapists, and not the 19 year old with an underage girlfriend) people in my area scared the crap outta me. Perhaps I should check again now that I've moved and have a child.
Edit:
Yikes. A guy a couple streets down had sex with a 7 year old. I knew I shouldn't have checked the site.
Another edit: The page said that contact happened more than once; he got 2 months in jail and probation. WTF????