"Topsy Influence measures the likelihood that, each time you say something, people will pay attention. Influence for Twitter users is computed using all historical retweets: millions of real, public statements indicating who's listening to whom. On our website, roughly the top 0.2% most influential of all Twitter users are tagged "Highly Influential", and "Influential" tags appear for the top 0.5% most influential Twitter users. So if Topsy says you are influential, you are part of a pretty small group!"If this is true, I can hardly believe I'm in the top 0.2% group of highly influential Twitterers worldwide, but I'm not going to ask for a recount!
You can read more about Topsy's standards here, and visit my profile on their website here. Also, hey, why not actually follow me on Twitter to see what you're missing? I'm so influential, I can probably make you do things with a simple 140-character tweet, such is my power... mwuahahaha.