And Americans (at least in MN) don't like folks who use the Governorship primarily as a stepping stone to DC. Just ask Mark Dayton. It sounds like she has a sympatico Lt Gov, so she's not really leaving Alaska in the lurch.
Bad press could make it look like quitting, good PR could make it look like a plus for Alaska and Sarah.
Time will tell.
I don't think that any fair minded person would label someone as an opportunist if they simply finished the term that they were elected to and then ran for higher office some two years later.
I think if Palin would have stood for reelection, and then announced just a few months after her second term had started that she was a candidate for President, that would have soured many people in her state, and rightfully so.
I really don't understand her logic. It seems likely that she doesn't have any more political aspirations. And, given what she and her family have been through the last year, I can't say that I blame her.