TunkRank is an influence ranking tool that helps you identify leading influencers on Twitter. There are two basic ideas:
As a twitterer, your influence does not depend on how many people you follow. However, your usefulness as a follower does. Having higher influence depends on having many followers who follow relatively few people but are followed by many. Followers like that are more likely to read your tweets and act on them (retweeting, clicking links, responding, blogging, etc). Their influence trickles up to you.
Your TunkRank score is a reflection of how much attention your followers can both directly give you and how much attention they bring you from their network of followers.