More to the point, are you judging the candidates fairly? It is well-accepted that when giving a prepared speech, Barack Obama is a fantastic presenter. Many would agree the his speech during the 2004 DNC vaulted him into the national stage and to the position he finds himself in now--running in a tight race for President of the United States.
It is also known that Obama doesn't perform as well in a more free-form setting--thus the jokes by the right about him bringing a teleprompter to the rodeos.
Below is a YouTube video (hat tip Kim Priestap) that has a few clips of Obama "off the teleprompter". If you want to give yourself a test try to put aside whom you have decided to vote for. Imagine if Sarah Palin spoke in the same halting fashion. What would the media reaction be? What would your reaction be? There's no one watching, so be honest with yourself if you can.
Normally when I read opinions that Obama has the potential to bomb during the debates, I discard them as partisan dreaming by conservatives. But if he doesn't rehearse his talking points more than he did for those speeches in the above clips, the negative impact could indeed be significant.