I think that anyone who values their privacy shouldn't be on ANY social network. I also think that anyone who thinks Facebook are the only ones doing this are kidding themselves. A friend of mine used to be a Myspace employee & she once said that if people knew what the company did with people's personal information, they'd be deleting their accounts fast.
Fact is, if you don't want your information out there, don't post it anywhere online. Plain & simple.