Why Sarah Palin, you ask?
Many commentators say the choice undermines John McCain's attacks alleging Obama lacks experience. I think he wants to reinforce those attacks. If you like her, then she's charmingly young and energetic, the maverick future of her party. Anytime her experience is made an issue, then the McCain campaign can happily point out that at least the more inexperienced candidate on the ticket is in the number two slot, not at the top like in the other campaign.
There is also an anti-Cheney ring to this. McCain may be trying to show that he doesn't need a VP to guide him - like Bush did, like Obama does? - and so picked a running mate who won't try to set the White House agenda.
McCain also offers Republicans a minority choice to assuage any guilt they might harbor in voting against Obama. There is a certain segment of the party that doesn't want to block the bid of the first viable African-American candidate for president. Now they have a minority candidate of their own to vote for - they can still tell their children that they were on the right side of history. This isn't about winning a certain number of votes, but it is about generating enthusiasm.
Her appeal to hard-core conservatives is another play at closing the enthusiasm gap. Being outside the beltway and outside of the mainstream - at least in terms of potential VP choices - may also burnish the maverick-y meme of the McCain campaign.
But all of this works only if Palin has McCain's respect. The choice has echoes of the trophy wife/young assistant storyline. Older man picks younger companion to show he is still in the game, still "with it" culturally and socially. But that's also a choice meant to leave the older man in control. It's a relationship in which he wants to give as little of himself as possible and still get what he wants in return. Republicans should worry the two will end up at odds. Will he resent her for trying to lay claim to her rightful place on the ticket? She is clearly ambitious. How will McCain respond when she tells him how to shape policy or steer the campaign? Will he accept her counsel gladly? Or bristle at being told what to do? This tension has a male-female dynamic and an insider-outsider dynamic as well.
McCain is a maverick and he wants to go it alone. He has a few close advisers he will listen to. The question now is whether he has the fortitude necessary to forge a believable-looking partnership with someone young, relatively inexperienced and highly ambitious. Because he clearly despises Obama for exhibiting these same qualities.