You only have to recall Susan Estrich's smirking face as she explained that the exit polls clearly showed the John Kerry had a commanding lead and would be the next President of the United States.
Here's one of my favourite sites for polling information: http://www.pollingreport.com/BushJob.htm
Notice that, when the poll is taken of registered voters or likely voters, the numbers tend to run two or three (or more) percentage points higher than the polls of the general population. I believe this is a consistent trend, so when pollsters want to report drastically lower numbers, they poll the general populace. My question, if they're not going to vote, why would we give a rats' rear-end what they think about politics? Every so often, a politician will claim to speak for them when they weigh in on one issue or another, but I would have to ask how they know? If they don't vote, how do we know (or why do we care) where they stand on any issue? My view is that, by being unwilling to participate in the electoral process, they say that they are willing to accept the decisions of others, whatever it may be (and, by the polls, accept it grudgingly).
In my opinion, you can pretty well disregard any poll that isn't limited to registered or, preferably, likely, voters.