A new census report of American migration between 2005 and 2009 shows that, well, Americans are mostly staying put, and if they are migrating elsewhere, they're not moving very far. Underscoring that fact is the finding that the only sizable group of Americans moving to Miami-Dade came from Broward County. However, Miami continues to be a hot spot for immigrants.
Of course, most American counties saw their greatest influxes of migration from neighboring counties during that economically depressed time.
So what actually makes Miami-Dade's stats unique (compared with the rest of the country, though perhaps not to our own history) are the number of migrants coming from different countries.