The hero of Walter Kirn's novel Up in the Air inhabits an entirely new state: Airworld, where the hometown paper is USA Today, the indigenous cuisine wilts under heat lamps, and the citizenry speaks a Byzantine dialect of upgrades, expense accounts, and market share Airworld even has its own nontaxable, inflation-free currency in the shape of bonus miles, which Ryan Bingham calls "private property in its purest form...