Social networking sites for sex?

Why would anyone ever sign up and pay for a dating site when there are so many free social networking sites on the internet today? From MySpace to Facebook etc etc the list goes on and on anyone that can upload a picture of themselves and fill out a profile can join any social networking site for free and starting looking for people in there area. Which is funny to me because recently adult friend finder sold for hundreds of millions of dollars and now sites are popping up left and right offering free social networking. Even twitter can be used as a dating profile if you wanted to tweet it.

My question to you is have you ever used a social networking site for sex? And if so which one?

Well for my yes I have used Facebook to hook up with a couple of past flames from high school and it was a blast doing so and catching up with people from back in the day. I still have not been able to find my real true love from the past yet but at this point I am really not looking because I have found the one I plan to be with the rest of my natural life, keyword being natural wink.