In fact, according to twitterlocal.net, there are roughly as many twitterers in New York City as San Francisco (on May 6 it was almost even). More in London UK

In fact, according to twitterlocal.net, there are roughly as many twitterers in New York City as San Francisco (on May 6 it was almost even). More in London UK than Los Angeles, CA. Almost as many in Wash. DC as LA. And Tokyo is the Twiteringest city by 3 to 1.