There's an interesting aticle on how the GOP became dominant in the South here. It helps to debunk the myth that the GOP gained the South through covert appeals to racism. It's an interesting article, and I highly recommend it.
I've lived in the South for 11 out of my 29 years. While there is racism in the South, it's nowhere near as widespread and pervasive as you would think by listening to Democrats. It certainly isn't the motivating force in the areas from which Republicans draw their strongest support. In the end, accusing Republicans of racial appeals is insulting to them, but it's the Southerners they're outrageously deriding. If Democrats want to win in the South, perhaps they should be less nasty to Southerners.