The fastest growing Twitter account as of now, I guess, is Google's official Twitter stream. Google joined Twitter on Thursday, 26 February--today.
I’m 01100110 01100101 01100101 01101100 01101001 01101110 01100111 00100000 01101100 01110101 01100011 01101011 01111001 00001010This was Google's first official tweet some seven hours ago. And what does Google's first tweet say? In plain English, Google said: I'm feeling lucky. You know where you see it almost every day.
While I was writing this post [15 minutes or so], some 300 Twitterers followed Google's tweet feeds. You can see in the screen shot that I had taken before starting to write this post shows some 6,290 followers. This went up to at least 6,600 when I went back to get the number of followers.
Compare it with Yahoo's 2,785 that joined on 9 February. And Yahoo's first tweet said "better late than never". So they have welcomed Google to this Twitter whirl.