Palin was not the problem in 2008

Yahoo: 

The Washington Examiner recently reported on an academic study on the 2008 presidential election entitled "The Palin Effect" that examined the effect of then Gov. Palin on theJohn McCain campaign. Its conclusions run counter to conventional wisdom.

The cliché, advanced by the media and the now infamous HBO TV show "Game Change," was that Palin helped to cost McCain the election because of her "controversial" personality. In fact, typical of most vice presidential running mates, Palin had a marginal but largely positive effect on McCain's standing with the voters. She certainly did not drive away independents and moderates, who along with Republicans approved and liked her.

This analysis pretty much tracks with the effect of a vice presidential running mate has for most presidential elections. Opponents of an opposing ticket occasionally make the serious mistake of focusing on the person on the bottom of the ticket. Voters make decisions on who to vote for by their perceptions of the person running for president.

The McCain campaign was hampered by a bad economy and a dysfunctional campaign that, after the boost it got from the Republican convention and the excitement generated by the pick of Palin, never seemed to get much traction. Palin was blamed for McCain's defeat by certain members of McCain's staff who were keen to shift blame, a meme eagerly picked up by the media which was just as anxious to stop Palin from becoming a threat in 2012.
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I think McCain was the main problem with that campaign.  He was winning until he reacted badly to the economy tanking.  He stopped his campaign and went back to Washington where he looked ineffectual.  That was not Palin's fault and she could have helped in some blue collar states if his campaign had not preemptively surrendered in those states.  She is still a powerful political figure despite being demonized by Democrats who act like Joe McCarthy going after communist when they hear her named called.