Are you kidding me?
It's not her age or her gender, though I do feel like McCain picked a woman just for the sake of doing so, and that's insulting. It's not that she's an outsider, allowing McCain to claim another victory for "mavericks." It's not that she is a former Miss Alaska or an aggressively nicknamed college basketballer, though I don't know why we're supposed to care. It definitely is her lack of experience, which flies in the face of reason, and her platforms. It's the way they're using basically the same words, the idea of change in D.C., when McCain has been an ardent supporter of Bush most of the time.
I had a PMS-ing week of tearing up to the DNC speeches, especially the feminist stuff, so I felt punched in the crotch when I woke up to the news of McCain's pick.
And stealing Hillary's momentum, or trying to. Fuck you. And especially if you are going to vote GOP because you're upset with the way Hillary was treated BY THE PRESS. There isn't some vast conspiracy to elect Obama, just a groundswell of legitimate supporters. Look at that effing football stadium last night. And yes, Hillary was clearly popular, too, and that doesn't mean she would have been a good pick or even accepted an invitation to be his running mate. You don't have to be a woman to be a feminist, and just because you're a woman doesn't mean you're pro-women. That's the choice we're facing.
EDIT: Because I don't write about politics intelligently, here's a couple links for people who do.