The first thing I thought of when I saw Obama smirk was Al Gore sighing in his debate with Bush back in 2000.
The smirk was not a slight facial tick, it was an outright smirk. It made Obama look less Presidential.
If you took a caveman and had him watch the debate, and then ask him who he thought the sitting President was, I doubt he would say Obama. He just did not seem Presidential tonight. He lacked the gravitas of the office. Romney seemed to have it....not on the level of Bill Clinton, but he appeared to have more of that gravitas than at any point of his campaign so far. It will be interesting to see how this effects the polls in the next few days.