Social influence measurement company Klout has reached a milestone, announcing that it has acquired over 2,000 partner-developers who utilize its API. This time last year they only had 300 developers using their API. The company reports that it now handles 500 million calls to its API per month, showing an improvement in call volume of over 1,000 percent over the past year. That’s a big improvement, no matter how you slice it.

Klout measures social influence on social networks such as Twitter, Facebook and LinkedIn and then produces a score based on a scale of 1-100 for a variety of factors. The scale measures true reach, based upon things like followers and friends depending upon how often they interact through @mentions, comments, likes and other factors. Klout also rates the likelihood that a message will be commented on, retweeted, or mentioned.

The growing company currently sports a number of big-name partner-developers, like ExactTarget, Radian6, Assistly, HootSuite, About.me and Seesmic. Those represent just a fraction of the partner-developers they have added in the past year.

Given the large amount of data that many social networks process every day, companies like Klout provide good tools for measuring social influence overall, but often have their own shortcomings and are not always perfect.