Trulia put together a fine looking interactive map
showing how people move across the United States. For any particular city, the map shows the cities where transplants came from. In addition it shows where people go to when they leave a specified city.
What is interesting is that San Francisco draws on all the major cities to fill it's vacancies, but the city San Francisco does not register on any other city's radar as a desirable place to live. Even people from L.A. would rather live in Oakland... Well, that probably requires a more in depth study of economics. San Francisco isn't cheap.via Trulia