Like Dave, I have little use for Twitter. Even if I did, chances are that others won't. As a consumer social networking technology, I think it'll be popular enough for fame and fortune to revisit Ev. But as an enterprise groupware technology, I doubt it will make it over the looming wall of…office complacency. Even more established technologies like blog and wiki are still scaling that wall.
Having it installed is not the problem although tyranny of the IT department is no joke. The problem is in getting people to use the tool. Unless you can build up a critical mass of users fast, the tool will eventually tossed aside from disuse and rotting bits.
Opt-in adoption of new technologies works in the consumer market but, in enterprise settings, the same will rarely work. The fact that social software's effectiveness depends heavily on wide-adoption also makes that weakness critical.
It's easy to idly project latest coolio technology into enterprise software market, as easy as pointing a flashlight into a thick bank of fog. Don't believe what you see is what you'll get.