It looks like fun. Basically you sign in with twitter, and Twilk creates you a background made up of the profile photos of the people you follow, or your followers, or both - however you want to set it up. The more you mention, retweet, or interact with someone, the more they should show up in your background.
I haven't decided if I'm going to try it or not, but it does offer a very unique background for everyone - unless, as someone said, you have the exact same followers and interact with them the exact same way as someone else does - highly unlikely.
