I recall Obama attempting to belabor the idea that Romney's tax plan didn't add up, but he never went beyond that, and in part it seemed that he hadn't prepared for Romney to have out a second thought into how he would make it work, when Romney clearly had. After that was established, Obama never recovered, and repeated his initial charge, to vastly diminished effect, throughout the debate.
I think this is important, if only because it offers a glimpse in Romney the competent man at the wheel, rather than Romney the empty vessel who showed up for the rest of the campaign. He'll need to bring out the former if he ever wants to shake the stigma of his previous loss, and again I don't know if he's got another campaign in him. But, there's little doubt he's capable of doing the job, that's never been the knock on Romney.