It has been a long story today, but understanding the limitations of polling is very important. It is my own feeling that the mass media don't have a clue. They keep harping on the national polls, which are only peripheral, and rarely, if ever, discuss the normalization for political party issue discussed above. They give the (highly misleading) impression that a score of, say, 49% to 41% means that 49% of the people polled were for the former candidate and 41% were for the latter. In reality, that result is the consequence of a lot of statistical massaging of the data based on a model that is rarely openly discussed.
So just remember to take ALL the poll results with a grain of salt. The only authoritative one (pace Diebold and other Republican shenanigans) is the one on the first Tuesday of November.