Marshall Kirkpatrick of ReadWriteWeb covers a new site that tracks Twitter:

On Tweeterboard you'll find not only a list of the top 100 most influential users on Twitter - you can also look up any of almost 2000 users and see who they are conversing with and get some idea how much influence they carry in the Twitter ecosystem.

From the site's about page:

Tweeterboard is a way of looking at who is influential on Twitter based on their conversations with other Twitter users. There are other services, like Twitterposter, that base influence on how many followers you have. Tweeterboard looks at who talks to you.

Looks like it might become popular among Twitter fans.