"I had students two years ago who did a project which is way more obvious now than it was two years ago; it turns out you can tell people are gay by analyzing their social networks."

This is one of the reasons I use social networking so sparingly. It seems like it would be fairly easy to do analysis based on a large stream of social networking information and use that to determine traits of a person that they did not intend to share. I'm sure that a lot of it is used for targeted purposes, like advertising, but it can also be dangerous. Maybe I'm just paranoid.