My first thought was that the polls are unreliable because the polling companies don't know who is going to show up to vote. Will the surge of Republican-leaners be very large? Will the counter-surge of Dem supporters be even larger? NO ONE knows this in advance, so no one can accurately poll. The polls are guesswork at this point--you guess who is going to turn out, and try to poll on those demographics.
It turns out that this impression (my impression of how polls are conducted) isn't correct. According to this detailed article, pollsters poll a random sample of everybody, not a chosen sample based on their hunches of who is going to vote. Pollsters learn who intends to vote only after running the random poll. Duh, that makes sense.
So perhaps the supposed skewed polls, the ones that "are in the tank" for Obama, well, maybe they aren't skewed. But don't tell that to diehard conservative paranoiacs. Their argument is that the MSM is terribly skewed, and it's not much of a step to posit that polling companies are skewed too. Thus, the need to unskew polls, which this site helpfully does by recalculating the sample to fit the demographics that are expected at the voting booth. Yes, those demographics that NO ONE KNOWS IN ADVANCE.
My conclusions: Doubts about polls are reasonable. Unskewing polls is ludicrous.