Nate Silver does the math on Palin. She has lower favorables than Hillary did at this point:

We're not in the business of saying "never" around here. Palin absolutely could become President someday. But it isn't very likely. If the Republicans nominate her (which is certainly possible), I think Obama could get away with having approval ratings in the low-to-mid 40's and still be at least even-money to win. That wouldn't be the case against Mitt Romney.

I think she has a very strong future in the GOP and will be a fixture for many years. She is the purest incarnation of Kristol-Rove conservatism: white, Christianist identity politics; borrow-and-spend economics; permanent war for Greater Israel, war against Iran; open-ended occupations of Iraq and Afghanistan; and a constant culture war irritant to keep the country polarized. What's not to like? They like their elections 51-49.