I think there is a long history, going back almost five years back to the start of the site where people got a lot of people on their "friend of" list because of a user icon. It has been studied before - I put up a journal with vacuous stuff with a really attractive bear as a user icon, and a banal journal, and it got about five times as many "friends" as another banal journal with a not so attractive bear.

While it's not exactly scientific, it is interesting.