Neither Palin nor Biden will make any big time gaffes or blunders. Biden will come off as likeable as he flashes his chompers while Palin will pull the "hockey mom" act that her supporters love so much. They'll both push for their guys while essentially avoiding any head-on collisions. One of them could get up on the table and do a jig and it will have little to no effect on the overall race.
At the end of the day the race will be about Obama vs. McCain, as it has been and as it will be.
UPDATE: From a political point of view this ad on Biden gaffes from McCain is really dumb. It basically sets up the idea that Biden will make a flub in the debate. The chances are pretty good that he won't, due to the stakes. The McCain campaign in the last 20 days or so reminds me so much of the Kerry campaign with the random flailing.
And mint julep Fred Thompson weighs in that Palin may be overcoached, and that explains her recent clunkers. Of course, Fred Thompson was lousy in the GOP debates so this may be a little like asking me to give color commentary on the 100 meter dash.