Here's a long, long opinion from the editors of some publication that says the red/blue, conservative/liberal divide is not coincidence.
http://www.urbanarchipelago.com/. It's all about the urbanites vs. the rural ppl. It's a very interesting take that I had not considered before. I have to say that after living in Austin for the past year and a half, that I find myself identifying. When I return home on weekends or holidays, the urban vs. rural mentality is more obvious to me now.