According to a new Census Bureau report, Americans are skedaddling from big cities and foaming up the burgeoning "exurbs," the outer rings around urban cores—a move driven primarily by housing affordability, or lack thereof. New York, for example, had a net loss of more than 210,000 residents per year between 2000 and 2004. The big metro gainers? In order of population gains it's Riverside, Calif.; Phoenix; Tampa-St. Petersburg, Fla.; Atlanta and Dallas-Fort Worth. --Mark Stuertz