In the Obamacan obsession that McCain's VP choice is all about them (and I include the MSM in this group), few of them are paying attention to the true impact of Palin's presence on the ballot. As always, events can change the calculations (just as the event of Palin's selection did on Friday), and I don't think we will have a clear view until after the Republican Convention, but some effects can be anticipated.
The political issue is bigger than Palin herself. There are a wide range of reactions to her selection and her ability to garner votes (as opposed to generate buzz) is probably narrow, though wider than it should have been. With regard to Democratic voters, putting Palin on the ticket should have had the same effect with Dem and Dem-leaning Independent women voters as putting Alan Keyes on the ticket would have had with Dem and Dem-leaning Independent AA voters, to wit, negligible. However, with the misogyny and Hillary-bashing of the primaries and the out-of-the-gate misogyinistic reactions to Palin herself, the Obamacans will suffer measureable attrition from this constituency. Among Hillary voters I have read and/or emailed with, most are laughing their asses off at the hysteria of the Obamacans, but most also are saying they won't vote for a conservative. A significant number who were considering voting McKinney or simply leaving the ballot blank say they will vote Palin. None who said they would vote Obama are changing their minds.
The new voters Palin is bringing in are on the Republican side, evangelical voters who were uninspired by or distrustful of McCain but who will eagerly turn out for Palin. The argument about McCain's poor health (which I think is both bogus and a bad, bad argument for Dems to make) is actually a plus for them, because it offers the prospect of one of their own as President. She will probably bring out moderate Republican women who would have gone for Hillary, don't really like McCain, and would probably have sat out this election round.
The real impact that Palin can have on the race is the way in which she compounds the effect of the Republican ticket. The huffing and puffing about her qualifications and experience has no effect on the Republican base. If anything, her ability to piss off the SCLM is a feature, not a bug. She is a Media Darling to them because the media hates her. She adds an extra exclamation point to the Republican argument with constituencies whose voting preferences decide elections. The focus on women voters, left and right, ignores that she may be a statistically significant draw for blue collar voters, especially those who are already somewhat culturally conservative. This is not so much that she will bring in voters that McCain cannot, as is the case with evangelicals, but that she reinforces his appeal to that constituency, and "seals the deal".
Where I anticipate her being a "game changer" will be in state and local races, where a slight increase in turnout can change results. When some races and ballot measures are decided by a few hundred votes, getting out twenty more voters here, eight more voters there will pay off. I don't think that this was one of McCain's considerations when he chose her, but it is most certainly a consideration of the state party officials who are dancing a gleeful jig. It may endanger governerships, state legislatures and some House races Dems were hoping to pick up. For example, Washington State will have a rematch of Dem. Gregoire and Rep. Rossi for governor. The last time, Gregoire won by a razor thin margin after multiple recounts that are not considered valid by the losing side. In news reports I have read, Rossi is very happy with the choice of Palin to help him turn out his own cultural conservative base (he is a truly bat-shit insane culture warrior who cleans up nice) and expects another close battle with Gregoire - which he will win this time. Washington state is far more conservative than people realize, and adding Palin may actually turn Washington red because of the makeup of the Republican Party. This may be repeated in red and purple states in specific races where the race is close.
The next consideration is for ballot measures and initiatives, such as the anti-Affirmative Action measures in Colorado and Missouri (among other places) and the anti-gay marriage state constitutional amendment in California. Palin now adds an appealing and energetic face to put on the GOTV efforts on the Republican side. Interest in her, her marketability, raises the viability of these policy measures. My second thought after seeing her name in the news as McCain's VP pick was that California will soon have anti-gay bigotry enshrined in the state constitution because she will bring out the fundies to vote for this measure. My third thought was that California is no longer a shoo-in for the Dems because of the way in which a telegenic, appealing cultural conservative candidate who hits all the right libertarian notes will herself be reinforced by the anti-gay marriage initiative.
Choices like Palin are risky. This may yet all backfire on McCain. What I see, however, is an accidentally savvy ticket selection that is generating buzz and will redound to the Republican's advantage in the fall. It may not win the White House for them, but it revivifies an otherwise tired and disaffected Republican base.
The deliberate actions of the DNC and their selected candidate to antagonize and alienate the Democratic base only compounds the problem.