We’ve partnered with Klout to add their influence ranking to all member profiles and have included it as a part of Social Pro (which is now FREE).
Klout is a service that measures your overall online influence based on a number of factors linked to your Twitter account. Scores range from 1-100, and the higher the score the wider and stronger your sphere of influence. In determining your score, Klout takes roughly 25 different metrics into account including true reach and amplification probability, and is even able to distinguish what type of Twitter user you are. (MailChimp is a Curator.)