The crew of old debater friends I've been watching with seem to agree with my impression that this was a clear Kerry win (I believe the word "assrape" was used) but a quick scan of the talking heads and bloggers suggests that most people seem to think their guy did the better job, so who knows. Looking back I see I've picked on Bush pretty consistently, which isn't entirely fair—those repeated invocations of Vietnam, as though the experience of shooting at VC on a riverboat is an experience relevant to being commander-in-chief—were silly, though less nauseous than at the convention. Still, there seemed to be more targets of opportunity on the right side of the screen. Whether it matters is another story; the recent meme has been that with expectations for Bush so low, his competent performance would be read as a victory. We didn't get that competent performance, but again, it's relative to expectations—since he managed not to sit there just jibbering, it's within the parameters of the "Bush isn't the most eloquent public speaker" narrative, so it's hard to imagine anyone changing their mind in response to an exchange that fit the established candidate stories well.
Addendum: It was pretty obvious that Kerry won in a formal sense, but I wasn't sure the popular reaction would reflect that. It looks as if it does, though: The ABC/CNN/CBS polls are all giving it to Kerry by margins of about 10 to 20 points.