ValdisKrebs analyses political book buying and finds strong clustering into two camps :  http://www.orgnet.com/leftright.html  http://www.orgnet.com/divided.html (See also SocialNetworkAnalysis)
RichardFlorida finds voters clustering into politicised cities : http://www.washingtonpost.com/ac2/wp-dyn?pagename=article&node=&contentId=A8229-2003Mar21 (See also CreativeClass)
This quote from Florida just struck me :
For much of the last century, the nation's politics has been dominated by geographic splits – North and South, rural and urban. Now, society is changing at a more molecular level. City by city, even neighborhood by neighborhood, our politics are becoming more concentrated and, consequently, more polarized.
This is a SystemEvolvingTowardsMoreSmallerSpecialistComponents