TwitterPoster is a visual representation of the influential tweeters. By influential, they mean the people with the most followers.

They say:

TwitterPoster is a mashup created from Twitter, the microblogging service owned by Obvious LCC (Blogger Xanga, Odeo). Inspired by ‘The Million Dollar Homepage’ and the populars tagclouds, the service generates a mosaic with the images of users who have a greater number of followers in Twitter. Each poster have 5 photos of 72×72 pixels showing at 5 users with more followers, 10 images of 48×48 pixels for those between the positions 6 and 15 (both inclusive) and XXX images of 24×24 pixels for those who are on the position 16 to 538.