Well, McCain sure tore things up.
Not that his Veep pick was entirely unexpected. Overall, I'd say Sarah Palin is a positive, though I doubt she'll make much difference. (Not making much difference is a good thing--I think it's easier to lose on a Veep pick than win.)
The two most obvious positives are pretty good ones. First, she truly seems to excite the base, something McCain needed to do. (At the very least, he didn't need to make a pick that gave them the finger, like Lieberman.) Second, she appeals to women, a group McCain needs to make gains in.
New England Guy writes the pick is bad because it "looks to be desperately pandering to disappointed Hillary-backers." No matter who McCain picked, she'd have to appeal to SOMEONE. This is generally considered a positive in a Veep. Should McCain have picked another aging, white, male Republican from the Southwest to show he was above "pandering"? (By the way, how can a pick be risky and pandering at the same time?) For better or worse (worse, I'd say), a lot of people are extra-excited about Obama because he's (half) African-American. Almost as certainly, some will be excited that a women might sit in the second-highest executive slot.
The truth is there are a fair amount of embittered Hillary voters (and just as many non-bitter women in general) who are not guaranteed to vote Democrat--for the McCain campaign to try to appeal to this important demographic is a smart move. That she sends a scare into Obama's people is shown by their reaction. They immediately sent out a nasty, dismissive comment about her, and a few hours later responded in a more muted tone, realizing, after the battle with Hillary and the Biden pick, they don't want to tick off women any more than they have to.
There are other positives but they're fairly minor: this steals the spotlight from the Obama speech and the Democrats' convention in general, and turns Labor Day weekend into a warm-up for the Republican Convention; it ratifies the belief that McCain is a maverick and not an establishment figure; it gives us an attractive, refreshing figure with many positive qualities and a good story that should play well; it gives a patina of freshness to the McCain ticket that was missing, and, when considered with the Biden pick, makes it almost as forward-looking as Obama's campaign.
But there are negatives, of course: McCain's campaign wasn't going badly, yet this is the kind of shocking move that usually comes out of desperation; presumably she's been vetted, but being a relative unknown, maybe she has skeletons in the closet; there's still some number out there that don't want to vote for a women (though, like race, it may be more than made up by those who actively do--plus this is only for Veep); she's from a small (electoral college-wise) state McCain's already won.
But all these are insignificant next to her level of experience. She obviously doesn't have too much--not enough to be President, many would say. And since McCain has made a big deal about Obama's lack, doesn't this take away one of his strongest weapons?
Well, yes and no, mostly no. McCain's people will have to tread lightly in this area, but it still plays. After all, we're talking about a Veep. Unless McCain dies in office (which is unlikely), she won't be taking over. And even if he did die in office, unless it was early in his term, she'd have a few years of the best possible experience for the job. In any case, if she were suddenly President (something I admit I've never thought about for any Veep before), she could pick her own Veep, and get someone with lots of experience.
But more important, her inexperience is a trap for Obama. McCain has to watch out, but this is twice as true for Obama (or Biden). Every time his side brings it up, the unspoken answer is "okay, she doesn't have enough experience, but neither does Obama--now which is worse, a Prez who doesn't know what he's doing, or a Veep in the same position?"