It's dull, annoying, and makes all the music on the radio sound the same. That said, I think T-Pain is a freakin' genius for coming out with an Auto-Tune iPhone app, and I am actually considering getting it.
And recording sea shanties in Auto-Tune.
Seriously, somebody needs to go record a medley of fifties doo-wop with this thing.
UPDATE: Okay, bought. Three bucks. I experimented a little during lunch. Sea shanties and whaling songs may not be the best, as the effect on "Rolling Down to Old Maui" was particularly horrible; a girlfriend once complained about my shanty-singing, but I guarantee her she'd've hated it even more if I'd been using Auto-Tune. Quick-paced Irish tunes might not be too bad, though; the effect on "Finnegan's Wake" was sort of interesting.