Your Twitter account has metrics. You knew that. The number of followers that a person has can be used as a measure of influence. On the other hand, that metric could be gamed by followlove, i.e. I follow you, you follow me and vice versa.
So here’s another approach from Tweeterboard (thanks @jowyang for the heads up): a reputation score based on "conversations" you have with others. So now it appears that the community has found attention and influence metrics for Twitter…now all we need is one for authority.
It’s the combination of all three factors that make an influencer influential (earlier thoughts on this).