A truly great comment from Zacksback:

When it comes to Palin, there's an intersection of sexism and age that the Republicans don't understand (which is why they keep crying sexism and wonder why it's not working).

For many Boomer women, the primary sexist experience of their lives is: "Those men gave the job to that guy instead of me, even though I am more qualified and/or have more seniority."

For many Gen X women like myself (and Palin is Gen X) the primary sexist experience is: "Those men gave the job to that clueless chick instead of me, because the boss thinks she's hot and/or will be a yes-man with no ideas of her own."

If, for some Boomer women, Obama's win over Hillary represents the guy they lost the promotion to, Palin's selection plays the same role for Gen X women. We've seen it: first the incompetent yet babelicious woman is promoted over her head, then the boss orders the attention of the entire team/department/etc. to focus on ensuring that "we" shield her from "mistakes" (or worse, we get blamed for her mistakes). Palin reminds us of when we got screwed by this sort of bullshit. And it shows in voters' response to her.