Iowa Imponderables
Jay Cost at RealClearPolitics methodically goes through the aspects of the Iowa Caucus system that show the unreliability of polling in advance of the event, particularly with respect to the tight three-way Democratic race.
It's probably a good thing to read and think about before the next batch of Iowa polls, particularly since one's coming out tonight that apparently shows the Big Three Dems in Iowa within three points of each other.