One hears this line from little boys who don't like to lose, but it's a little surprising to hear it in the context of a Presidential debate. Still, GWB was also accused of "cheating," so I suppose it's always the default assumption when a conservative whips up on a liberal in a battle of ideas. (After all, we're supposed to be disarmed.)
What strikes me about the charge, though, is that it is flatly incompatible with the other excuse for the Obama loss: that Mitt Romney lied, lied, lied with every thing he said. You don't need to smuggle in a day planner full of facts if you're just going to make stuff up. The only purpose a "cheat sheet" would serve is making sure that you accurately remembered the facts you wanted to cite, so you wouldn't give your opponent an easy out by misquoting something you had mis-remembered.
So which was it? Did he cheat, or did he lie?