From a Colorado focus group:

Even more dramatic was the shift in the voters’ personal reactions to the two candidates. Before the debate, McCain had a 48/46 favorability rating; that improved to 56/36 by the end. But that’s about where Obama started the evening—54/36. After an hour and a half, Obama’s favorability numbers were 80/14. As Joe Biden would say, let me repeat that: 80% of the undecided voters had favorable views of Obama and only 14% saw him negatively for a net rating of +66. Not even Bill Clinton got such a warm response in town hall formats.

http://www.time-blog.com/swampland/2008/10/they_liked_him_they_really_lik.html