First, I think Robert Farley all but nailed the GOP strategy's gender politics:
The choice of Palin over any number of vastly more qualified women on the Republican side also tells us a bit about how McCain interprets the candidacies of both Clinton and Obama. McCain thinks that Clinton and Obama are both, essentially, affirmative action hires; they rose to prominence not because of qualification or talent, but rather because the one is a woman and the other is black and the Democrats go for that kind of thing. The antidote? A woman; any one will do, since (in the Republican view) you're already throwing qualification to do the job out the window when you eschew a gnarly white dude. |Lawyers, Guns, and Money|
And the only thing I would add to this is that it understates the warm fuzzies that some GOP voters are going to feel when they vote for a woman, any woman. There aren't that many people who want to think of themselves as racists or sexists, and putting Palin on the ticket gives moderately conservative voters an out. Now, instead of fretting about making common cause with the 'no hussein' crowd, they can focus on the fact that they're voting for a woman. As Farley said, it's still a qualification free affirmative action vote, and these voters oppose affirmative action, but there you go.
Second, there's been talk about the way that this undercuts the experience argument, but I think it's even worse than that. The experience argument was, among other things, a proxy for national security. It was necessary, first for Clinton and then for McCain, because Obama's actual views on national security are more popular at this stage than any sort of hawkishness. Once the experience argument is abandoned, McCain literally has nothing effective to say about national security.