Tuesday, January 22, 2008 - "The general process of suburbanization is, the richer you are, the more likely you move to the suburbs," says Julie Martin, a senior demographer for the Weldon Cooper Center for Public Service at the University of Virginia.

In the case of Washington, D.C., she says that well-paid government employees, and the area's lobbyists, lawyers and other tangential personnel, are "suburbanizing like mad" and in doing so have created a "feedback loop," driving more money into the area's suburbs by populating them with higher-priced homes and better school systems.

This often results is significant income differentiation among neighboring counties. In Forsyth County, Ga., for example, the median household earns $83,682 a year, about $33,000 more than Fulton County, its immediate neighbor. The more a county becomes an established bastion of wealth, the more residents from the surrounding areas want to move there, driving up prices for homes and creating superior tax-based services.

-Matt Woolsey/Forbes Real Estate