The Audacious Epigone has a long critique of Red State, Blue State, Rich State, Poor State. The main criticism is that Andrew Gelman did not emphasize the affect that race has on voting patterns enough; a criticism brought to sharper focus by the 2008 election.
We need 2004 exit polling data on whites by income to see if there really was a seismic shift not only in where white support was most concentrated for the GOP, but also a shift across the country of poorer whites being more likely to vote McCain than they were to vote Bush, and wealthier whites being less likely to vote McCain than they were to vote Bush.