The 2012 presidential election will be a nail biter. But even if it was a potential runaway for either Obama or Romney, the vice presidency would still be important. Obama knew it and picked Biden. McCain missed it and picked Palin. Romney won't miss this and will pick a boring white guy.
Given McCain's age, medical history, and the possibility of a debilitating episode that would leave him unable to fulfill the duties of the office, the chance of a Palin presidency is about one in four.
Hillary Clinton is being talked about as a possible vice president; her supporters say she is the strongest choice, and that anyone else is inferior. But Al Gore is certainly the most qualified for the job.