There can be no better example about how crazy polling has been this year than the recent Pew and National Journal polls. Both were taken over the exact same period of time. Both had the data collected by the same company - Princeton and Associates.
Pew had the race at 47-47, with Romney having a decided turnout and enthusiasm advantage.
National Journal had it 50-45, in favor of Obama, with the internals favoring Obama.
Likely very similar sets of raw data, two very different assumptions as to the likely electorate.
you have the same data from the same people and you get different results the answer is somebody changed the answer!