Politicos often talk of voters along a 5-point scale in which 1's are loyalist Democrats, 2's are weak Dems, 3's are Independents, 4's are weak Republicans and 5's are loyalist Republicans.
Palin will help unite the GOP (in fact, she already has). As such, she will shore up McCain's support among the 5's (base Republicans who care about God, Gays and Guns) and will activate the previously weak support McCain received from evangelicals who's actual willingness to turn-up for the Republican in a Presidential election cannot be guaranteed.
On the other hand the Palin pick may well play poorly with 3's who value experience, national security and a moderate stance on social issues. If these voters are concerned about Palin's credentials to be a 'heartbeat away from the Presidency' how much more so the Hillaristas who will loathe her opposition from everything from a woman's right to choose to the use of contraceptives by married couples?
In other words, the Palin pick is not so much about women as it is about evangelicals. In this McCain has been clever, he has made a base-pleasing Veep camouflaged as an appeal to ex-Hillaristas.
This raises some interesting implications for the electoral map, especially in the evangelical-heavy areas of Ohio, Colorado and Virginia as well as Obama long shots like North Carolina and Missouri. I'd be interested in readers thoughts on that as I gather information for my next electoral vote analysis - thanks!