Klout is turning Twitter into a game. As you tweet and connect with other Twitter users, you earn badges for notable achievements. For example, when you're mentioned by 100 unique users, or have a message retweeted by 25 people, your Klout profile gets a pretty new graphic. The data behind this can be used to determine influential Twitter users.
Klout uses Twitter's API to analyze user data. In addition to the achievements, Klout also classifies users into one of sixteen influencer types, such as curator or socializer. You can get a feel for how the site works in the screencast embedded below.
Despite the game-like achievements, the service isn't just for fun. Over 250 companies are using Klout to find influential users, according to TechCrunch. Most aren't using Klout via its website, but instead its own Klout API, which provides influence scores and classifications. For example, CoTweet shows the influence rating to its users, who may be performing customer support. A complaint might be more likely to be elevated if the customer has a higher Klout rank.
At first blush, Klout may seem like the PageRank for Twitter service we wrote about. While both mine data for meaning, Klout looks for influence, while Trst.me aims to emulate the algorithm Google may use to rank users.