Geographic mobility costs are a drag on the economy, because they slow and/or truncate relocation of labor to shifting areas of demand (a good example is the fact that North Dakota currently can't get enough workers because people can't/won't move there to take advantage of the opportunities.
Apparently, there are economists who make the argument that one reason for the post-WWII boom is that the war increased mobility for a variety of reasons, not the least of which was the forced extrication of young men from their homes via the draft. Apparently Hurricane Katrina may have had the same effect, blasting people out of the moribund New Orleans economy and forcing them to move to more dynamic areas.
This is probably true, but also one of those areas where economic analysis falls short of total well-being analysis (for lack of a better term). I know folks from New Orleans and they often seem to be deeply tied to the New Orleans culture and miss it when they have moved away. Many move back. So just because someone is better off economically with a job in Houston does not necessarily mean they consider themselves better off.