Well first, unless the economy improves in a very substantive way between now and Oct. 2012, the Easter Bunny could beat Obama (probably). But, there are some specific demographics challenges Palin needs to over come, somehow, if she wants to unseat Obama, absent some kind of additional economic meltdown.
Latinos are problematic. She polls even worse than McCain with Latinos. They hate her. Obama would move from 72% Latino support, to something approaching his black support, 95%. George Bush did almost 18 points better with Latinos than McCain did. And, they'll be an even bigger percentage of the electorate in 2012.
Young people. They hate her too. Unless the next GOP nominee can cut into the youth vote enjoyed by Obama, it makes it that much more difficult to beat him.
And women. For whatever reason, Palin under-performs with women across the general electorate. Even in this poll - polling Republicans - her percentage of support is the same amongst men & women - 17%. You would think the female candidate would do much better with Republican women, and women in general. But, she doesn't.
Gov. Palin has massive support.