Princeton's Sam Wang's Electoral College Model – bang on in 2008 – sees a spike in state polling for Obama. His attempt to explain the discrepancies between state and national polling is worth a look as well. Money quote:
BOTTOM LINE: Even if national and state polls have the same flaws, they are consistent with one another. Because state poll aggregation is so powerful, the result based on state polls is likely to be more accurate. That is what I would call The Math.