The Myth Of The Maverick
As almost always, Ezra Klein makes a good point:
Sometimes I don't think it's fully appreciated how constrained the GOP is by its pro-life orthodoxy.
His point? VP candidates who not only would have been good political choices but would have actually been good possible Presidents (the whole purpose of that job) for a 72-year old Presidential candidate. He mentions some, I'm add a few others:

Joe Lieberman: -- I hate the guy to pieces, but what a story it would make -- hey, McCain IS a maverick, and loyal to his best friends. Party politics Lieberman is a former VP candidate himself and 'fully vetted' as they say. He essentially has left the Democratic party and could easily tell (maybe not sell) a message of the party leaving him, blah blah blah. I'd hate it, but that's probably a good thing for Crusty McCain. His downside? Aside from being a former Democrat and being Jewish, Lieberman is pro-choice.
Charlie Crist: The very popular governor of Florida is also one of McCain's best buddies, and McCain simply can't win the election without the Sunshine State. The problem? Crist is pro-choice.
Tom Ridge: Hugely popular in Pennsylvania, another crucial swing state. Former Director of Homeland Security (he's the one who came up with the ridiculous color terror alerts) and probably great on the campaign trail. The problem? Ridge is pro-choice.
Kay Bailey Hutchinson? Jodi Rell? Klein mentioned these and I know less about them, though they obviously have the benefit of being a woman VP pick, a political move clearly designed with Palin. Their problem? They are both pro-choice.
McCain gets some legs out of people mistakenly thinking he's pro-choice, or at least would respect the law of Roe v. Wade. That might have been true in 2000 as far as the law is concerned, but McCain has an amazingly solid record of being anti-choice. This selection of Palin is not only a grasp at a political gain at the expense of policy (he is running for Bush's third term!), but a solid reinforcement that he, and the current Republican party, can't live with a pro-choice candidate. This despite the fact that about 60% of the country wants Roe v. Wade upheld as federal law.
If McCain had nominated any of these folks, I'd probably be a little concerned about the political strategy and dreading the next few months of campaigning and listening to Lieberman, or Ridge, convince reporters that they are really the voice of reason.
I know Palin isn't a completely useless candidate - and I bet I'll be impressed by her at times during the season. But she's essentially a very unserious choice here, and that does indeed evoke memories of Harriet Miers. (Dan Quayle was an elder statesman compared to Palin. As is Obama.)
I'm sure that the press will be swayed by 'Maverick' McCain's choice here. It's almost exclusively designed for that, to woo woman voters, to ignore the reality that he's choosing her to be the leader of the free world if anything happened to him. Look, I don't LIKE pushing the age card (okay, I do a little) but it's pretty obnoxious to take someone this inexperienced and put her that close to the presidency. It goes against everything McCain has been saying about Obama, which shows how purely craven and political McCain is.
The Myth of the Maverick is dead and gone.