In 2004, the first exit polls that came out showed Kerry winning Ohio by 4 and Florida by 3 and he lost both states. Those same leaked poll numbers showed Kerry winning Pennsylvania by 20 points when he ultimately only won it by 51% to 49%.

Long story short: it would be more unusual for the exit polls to be right than wrong, so if some numbers are leaked out this afternoon and McCain isn't doing well, don't freak out.