This is an old slam of Hillary's she used in the primaries a few months ago. It didn't sink the Obama campaign then, it's unlikely to make much of a difference now.
In fact all the tv pundits seem to be chalking up Palin's attacks to desperation on the part of the McCain campaign, and for good reason: he's consistently been 5-10 points down in the critical swing states. None of his recent stunts (suspending his presidential bid etc) have succeeded in reversing that trend; if he isn't able to find a game changer soon, he will lose the election.
Plus we're 30 days out from a presidential election; this period is always vicious. *listens to Obama/McCain advisers tear each other's eyes out on CNN*