I stayed up way late attending PAX, so I had a hard time making this point in a coherent fashion. Polling shows that men reacted more favorably to McCain's VP announcement than women did. Men are, of course more likely to favor Republicans in the first place, so it's quite possible that what we're seeing is the electorate responding to demographic characteristics that shape political opinions.
This is, I think, bad news for Barack Obama. On the minus side, undecided voters are more likely to be whiter, over age 50, and not hold a college degree. On the plus side, they're somewhat more likely to be Hispanic and much more likely to be female. But the negative factors appear to outweigh the positives.