White women have moved from 50-42 percent in Obama's favor before the conventions to 53-41 percent for McCain now, a 20-point shift in the margin that's one of the single biggest post-convention changes in voter preferences.
That 20-point swing is pretty remarkable, clearly a testament to Palin's presence on the ticket. Having said that, I think it's actually somewhat reassuring for Obama. As I said earlier, I don't think Palin fundamentally scrambles the demographics of this race. In particular, don't see any way the most anti-abortion ticket in recent memory is going to win white women comfortably.
Once Palin's extreme anti-abortion positions become known (no exceptions for rape or incest!) and her halo wears off, I fully expect Obama to at least pull even among white women, which would give him a couple-point cushion in this poll.
Update: A commenter points out that Bush beat Kerry among white women by about 10 points in 2004. That's true, and fair enough. But it's hardly the norm. Kerry did unusually badly among women in 2004--winning them by a mere 3 points overall. In 2000, by contrast, Al Gore won women by about 10 points overall and tied Bush among white women. (Gore and Kerry lost men by an identical 11-point margin.) On top of which, the McCain-Palin GOP is, believe it or not, much more anti-abortion than the Bush-Cheney GOP. Phyllis Schlafly has called the current GOP platform "the most pro-life ever."