Speaking of which. Who remembers '04? Howard Dean was supposed to win the DFL nomination then the primaries came and Kerry won. Just goes to show. Politics is a hard game to call and don't shoot the horse 'til he's dead.
Picking a winner between two people within the statistical margin of error, or between the two in first and second can be difficult.
Determining whether someone has a chance to win is relatively easy to predict. Polls are very accurate when considering this figure.