There are only two metrics that matter: One, the President's approval rating (somewhere around 48%) and who is leading among Independent voters (Romney by at least 10%). In 2008 Obama got between 52-53% of the votes of Independents and ended up with about that much of the overall vote. If he's not leading on Election Day with this key demographic he will almost certainly lose the election.
The other key is his approval rating. In the modern American presidency most incumbents (in a two-man race) usually end up receiving an aggregate amount of the national vote that is about equal to his approval rating. If this holds true in 2012 (and there is no reason to think it won't) Romney probably beats Obama by about five points.
If political Independents continue to break to Romney he has a chance of a very clear win (52-54% and around 320 EVs). His huge win in the debate has turned the tide in the election, and, if it were held today, he would win. We'll see if he can hold on until Election Day.