One such confounding factor gives me some comfort. I think the polls will tend to miss the full effects of recent negative discoveries about Obama.
Consider potential new young voters that were impressed by Obama back before Rev Wright became infamous. They registered democrat and voted for Obama in the primary...but then the blush came off the rose, and they concluded Obama was just as slimy as the other politicians. So they tune out...and Nov 4 just comes and goes like any old day.
Despite them no longer participating, they are still a registered democrat. No pollster calls, because being new young voters, they aren't listed, or don't have a land line, or they work a service job and weren't home at dinner time. However, the pollster calls older more dedicated registered democrats on their behalf.
The polls are ignoring the huge percentage of Democrats who will show up and vote McCain/Palin.