Here is an interesting interactive map on migration from county to county within the US.
http://www.forbes.com/2010/06/04/migration-moving-wealthy-interactive-counties-map.html
(http://www.forbes.com/2010/06/04/migration-moving-wealthy-interactive-counties-map.html)
We get a lot of inbound from S. California and northern FL.
In the North East almost all the Red lines are to warmer climates. Very few black lines going to the north east. When you click on southern California there is a huge black line from the north east and red lines to almost everywhere else in the country. One of the things around here is if you click on the Poconos you can see the massive influx of people from NYC.
Neat. It's been updated and includes more info now.
http://www.forbes.com/special-report/2011/migration.html
Your map is much more interesting than mine:
(http://www.flickr.com/photos/7935459@N05/6489249085/)
Where are you going? (http://www.flickr.com/photos/7935459@N05/6489249085/) by Alan Gage (http://www.flickr.com/people/7935459@N05/), on Flickr
Alan