I remember watching a documentary that claimed that a good deal of the economic success of the US in the late 19th and early 20th centuries came from the fact t

I remember watching a documentary that claimed that a good deal of the economic success of the US in the late 19th and early 20th centuries came from the fact that it had a mobile workforce able to move to where the jobs were -- benefiting from a flexibility in terms of location, if not expertise. Of course, the complexity of modern technology creates a demand for increasing levels of human specialisation these days, and real-estate prices make it much harder to move across the country than it was 50-100 years ago. (Having said that, the last 3 years have seen me working in London, New York, and back to the UK again, so perhaps we are just as mobile now as we ever were....)