Its not so much a gaff as it is that sarcastic smirk Bush gives at the end of a point he is trying to make. Then the head nod too...not good body language.
Yes, Obama says "uhhh" a lot! But overall, his body language is much better. I don't like it when he gets into semi-preacher mode, like he has done at some of the campaign rallys. I prefer the way he talks in a more formal setting.