Room For Debate argues over slowing American mobility. It has decreased substantially since the recession started. Bill Bishop is worried about our migratory patterns:
People have moved to be around others like themselves, so most American communities have also grown either increasingly Democratic or Republican since the ’70s. (This trend continued through the 2008 election, by the way.) Party affiliation is a minor part of what is becoming political inequality. We’re really sorting by way of life and that is correlated with how we vote.
Andrew Gelman has a different take.
The Dish 