In the past 20 years, there's been all kinds of research about declining community life in America. Participation in PTAs, civic clubs, even bowling leagues is on the decline, and Americans don't really know who their neighbors are anymore. My guest today argues that what we're seeing is a transformation in how people organize themselves socially. Why people are doing this, and how it affects our society, is what author Marc Dunkelman ("The Vanishing Neighbor") and I talk about.