We are also dealing with a record number of new registrations, demographic changes, voter fraud, intense passions on both sides, low % of undecideds, outside influences (UBL et al), etc.
I am not a pollster, these are assumptions I arrived at by reading hither and thither during this crazy election cycle. I think a good article on the 'Net that puts pollsters in perspective is offered by JayCost:
Thanks for the reference to JayCost, it was very informative. Zogby is losing all creditability.