The chatter is all about how Gov. Palin's inexperience will undermine the McCain campaign's ability to hammer on Sen. Obama for his inexperience. The comparison seems a little odd, though. If McCain is elected, she'll be picking up highly relevant experience very rapidly, in the low exposure role of VP. Obama won't have that luxury.
But there are two possibilities we must consider:
1) The William Henry Harrison scenario: McCain could, in theory, arrive in Washington be inaugurated on a cold and blustery day, give a 2-hour, 8,444-word speech, and succumb to pneumonia a month later, leaving Palin with 3 and 11/12 of a presidency to serve and nothing besides these parting words: "Madam, I wish you to understand the true principles of the government. I wish them carried out. I ask nothing more."
2) The Battlestar Galactica scenario: McCain could also be killed when the Cylons return and wipe out most of humanity with a nuclear weapon. In Battlestar, the 42 officials in line ahead of Secretary of Education Laura Roslin fail to check in, and she assumes the presidency. She has no foreign policy experience, either.