My response to the McCain gas prices ad was similar to Jason's--that is, I think the "O-ba-ma" chants in the background are at least as important as the (absurd) policy dig in the foreground. But where Jason hears contempt in the ad (and in some of Mark Salter's comments about Obama), I hear something slightly different: resentment.
The storyline that seems to be taking hold a bit is that Obama is the golden child, the popular kid, the one whose every comment or action is immediately the News of the Day. McCain, by consequence, becomes the overlooked hero, the hard working, long suffering man of substance who can't compete with the shallow charisma of the Shiny New Thing. (Note: I don't think this characterization is remotely accurate; but it's the vibe that seems to emanating from the McCain camp.) These were, of course, the roles that Obama and Hillary Clinton found themselves in during the Democratic primary, but they must be more disorienting still for McCain, who's always been the popular guy, the wisecracker, the rule breaker.
Playing the resentment card against Obama worked pretty well for Clinton, but it's far from clear it will work as well for McCain (if, indeed, his campaign continues to play it). For starters, the fact that Clinton is a woman enabled her to give a deeper resonance to the idea that she was being unfairly overlooked. (McCain may benefit to some degree from a similar effect with older voters.) But at least as important, Clinton had a policy profile that fit neatly with the concerns of voters who might feel they were being overlooked (even if it was almost identical to Obama's). McCain, by contrast, has upper-bracket tax cuts, long-term war--and a few gas-related panders that everyone paying attention knows will have a negligible impact on prices at the pump.
Moreover, while everyone is irritated by the overpopular kid, an awful lot of people want to be him, or failing that, be close to him, in the same way that people like to be fans of winning sports teams. If McCain and Co. can't find a way, as Clinton did, to connect their appeals to resentment to some larger narrative, it risks coming off as mere envy. And that's not a winning political message.