Grammarians and journos take note: Twitter has made it as an entry in the 2009 edition of the Associated Press Stylebook, which is, of course, the gold standard for many newspapers and online publications (such as the one you are reading -- telling us to do such things as italicize words as words, such as the previous use of Twitter).
The guide notes that the microblogging service limits messages to short Tweets. The verb forms are "to Twitter" or "to Tweet."
The guide also added the verb form of text -- "to text," "texted" and "texting" -- as well. The AP seems undecided on what to call Twitter users, and has not included an entry for Twits.
This news may not be of much interest to anyone beyond those who are also really jazzed that the new edition of AP also now makes clear the differences between coma, minimally conscious state and vegetative state. --John Capone