Twilk is a service that allows you to creatively use your followers avatars. In fact, Twilk will make a Twitter background using the avatars of your followers. Simply sign-in to allow Twilk to grab your follower avatars and click “use background” once Twilk is done. A preview of the avatars will be displayed beforehand. The background will also feature a Twilk ad, which you have to pay to remove.
Choose between the people you follow and the people that follow you, or a 2 column and even black and white only background. There are numerous choices. To change the background you must revisit the site, it does not update automatically as you change who you follow or as new people follow you.
I was about to ask how placement is done for the background and they had the answer right there on the main page!
How are people arranged on the background?
People are sorted by how much you mention their user name ( @ replies, retweets, etc ) in your Twitter feed. It goes from top to bottom starting in the first two columns on the left. If you mention people the same amount (or not at all), the order of those people will be random.