ComScore's Media Metrix released global numbers for March and worldwide visitors to Twitter - reporting a 95 percent jump in the March from 9.8 million [Feb'09] to 19.1 million. 9.3 million visitors were in the U.S. alone.
These numbers only count visitors to Twitter’s Website and do not include desktop and mobile clients (big number of visitors) so the numbers could be much bigger. This growth was also helped by Ashton Kutcher’s race with CNN to one million followers, and Oprah’s subsequent adoption of the service.
With this kind of growth Twitter will hit 50 million visitors in a month or two. If you're interested in tuning in with Twitter, we would advise you to subscribe following tweets and use our tweet streams to find tweets from industry executives - note that AMD is especially active in the twittering arena: