During the primaries, Chuck Todd observed that in states with higher black populations, white voter support for then-Senator Obama was significantly lower. And this turned out to be accurate in the general election according to a study by Professor Charles Franklin at Pollster.com.
Alabama and Mississippi, in particular, show the highest African American turnout -- and the lowest white support for the Obama-Biden ticket. This doesn't necessarily prove white racism of course, but it points in that direction when stacked up with other exit polling data.
Here's one big reason why this is important: with this information in hand, Republicans will absolutely crank up the volume on the Southern Strategy in these states -- use race to scare white voters into sticking with the Republicans irrespective of economic factors or Obama administration success. That's the evil beauty of the strategy -- it works despite, you know, reality.
Adding... In other words, where there are relatively equal white and black populations, it's easier to say: "Look out! All those black people over there are going to take your job and rape your wife. Be afraid!"