One of my friends and I once posted each other on some online personal/dating services as a joke. At one point (while I was briefly single) I met one of the guys who responded. He was a nice guy, just not someone I wanted to date. He wasn't some psycho or anything, just a normal person. But I have gotten some weird responses, like right now I have a guy trying to get me to move to Boston or at least fly out there and visit him. No way that's happening.
I think you have to be kinda brave and daring to actually meet the people and if you do, then you should have someone around that you trust to watch your back and make sure people know where you are/what time you'll be back so that they will be alerted is something's not going right.
Just my experience. But overall, I think they're just a sad ploy for attention. I doubt that I would have put an ad up seriously looking for someone, I'd have to be pretty desparate.
~Chelsea