Bill Bishop takes up the question of political segregation in The Big Sort. He reports on the work of Penn political scientist Diana Mutz. She found that only a quarter of Americans say they regularly discuss politics with people who disagree with them. This is more than in some countries, such as Britain, but less than others, notably Israel.
Even more interesting, I think, is Mutz' finding that this average varies quite a bit depending on your social class. The least educated people have the most diverse group of political discussion mates, whereas people with graduate degrees are the least likely to talk politics with people who disagree with them.
I can testify to how easy it is for conversation among academics, the most educated group of people, to turn into a one-position echo chamber. Liberalism is taken to be an IQ test, and the rare conservative is encouraged to be quiet or go elsewhere. For political disagreement I go to the coffee house, which in our town draws a broader range of people than the faculty club contains.