Romney won on presentation more than anything else. He looked fresher. The president was stumbling his words and falling back on the same talking points he used earlier in the campaign. I don't buy the "anniversary" excuse, but maybe all the maritals he had that afternoon wore him down a little. Romney wasn't anything great, and his positions are more confusing and inconsistent than ever, but the president clearly had an off night.
That said, I doubt this will have a major impact on the election. John Kerry destroyed Bush in their debates and it didn't impact the polls at all. Lloyd Bentsen embarrassed Dan Quayle, but we all know who became vice president.