Using state level exit polling data from both the '04 and '08 elections allows for a more accurate table to be presented than national exit polls do. Only one in five of those surveyed at the state level participate in the more detailed national poll. The absolute votes (in thousands) and percentage increases in voters from '04 to '08, by race:
White turnout appears to have increased slightly rather than marginally decreased as national exit polling suggests. Because the '08 national exit poll inexplicably reported 9% of voters to be Hispanic, even though state level polling data suggests it was slightly under 8%, the 16.5% Hispanic increase suggested by national exit polling numbers is attenuated to a more plausible 9.9% increase. Even in a lackluster election for the white electorate, the absolute increase in white votes probably surpassed the absolute increase in Hispanic voters. The Hispanic vote just isn't very important.
Little stake should be put in the Asian and Other categories, because their numbers are so small in so many states. In Washington, for example, the '04 exit poll shows 2% of voters to be Asian, while '08 shows 3%. That translates into an incredulous 25,000 more Asian votes in the state this time around compared to the '04 election.
Using data from state level exit polling for both elections, the proportional representation of each racial group:
In addition to a shifting of the entire electorate against the GOP, the '08 results are largely the story of many uninspired white voters and a very inspired black electorate.
Keep in mind, too, when thinking about this, that exit polling consistently overstates Hispanic turnout.