A USA TODAY/CNN/Gallup Poll phone poll of "1,510 of the 470,000 people from Louisiana, Mississippi and Alabama who registered for help after the storm". They asked if they were going to move back, and:
Among New Orleans residents, 39% say they definitely or probably won't move back. The Red Cross registered more than 132,000 of the city's 180,000 households, which translates to about 50,000 households planning to relocate.