I am suspicious of all social networking sites. I don't trust them, and I don't trust my data being collected. There's too much of it and it's getting too powerful.
Well, that's one way to look at it.
Another way to look at it is, what data exactly is being given to social networking sites? The only data of mine that facebook could possibly find of value would perhaps be my gender and the pages I like... and I am quite willing for absolutely anyone in the world to know what movies, books etc I like. It's not a secret.
Besides that, I don't give them my last name. I don't give them anything that could identify me as me. I'm careful about what I put out there, so I'm not paranoid about which data they have.