First it's the Hilary's video on her website announcing officially her running for presidency, then it's the "anti-Hilary" 1984 video on YouTube, and now it's Obama on Twitter.
I don't know if it's the doing of Obama's campaign committee or simply one of his fans, most likely to be the latter, but we gotta admit the whole 2008 Presidential Campaign has just become a whole lot digital :) Cheers!
FYI: Hilary is not on Twitter, yet.