It scares the hell out of me.
I read message boards where people constantly post crap like, "I've got a date with this myspace whore this weekend" or "Check out this myspace chick. She lives right down the road from me. We're IM'ing right now. Gonna ask her out and nail her this weekend!" It's basically a place where people can hook-up online.
I've seen on the news where parents were convinced that their child's activities were innocent, so the news station ask for permission to try and arrange a meeting with the parent's daughter without her knowing it was a set up. After only a few minutes, the news station successfully arranged meetings with under-aged girl. It's a joke.
If I had children, I'd be terrified of that place. I'd do everything I could to block that site (and others like it) so they couldn't access it from home.