2. New York
New York is among the most expensive cities in the world and competition is stiff in every sector. Given the high cost of food and housing (and the freaky subway rats), the New York area's population is understandably somewhat transient.
According to U.S. Census data, almost 300,000 New Yorkers move to the suburbs each year, and nearly 200,000 relocate out of state. Their main motivation in leaving is to buy a home and gain more space.
But maybe it's at least a little surprising that the metro area they most want to flee to is Boston — which isn't exactly cheap or spacious.