Philip Klinkner of PolySigh compares polls from 2004 and 2008. One of many interesting observations:
Among older voters (the other age categories didn’t exactly match up across the two data sets) McCain is running much stronger than Bush. In 2004, Bush won this group by just 5 points, but McCain is winning by 12 points. This is no surprise since Obama’s support in the primaries was always weakest among this group, due at least in part to his race.
On the other hand, Obama is running no worse among whites overall than Kerry did in 2004, suggesting that if he’s losing any ground among older whites, he’s making it up among younger whites.
Caveats for taking early polls too serious apply.