I'm at work and don't really have a lot of time to peruse through, so talk amongst yourselves about it. For my state, I found out that Hattiesburg and Gulfport-Biloxi are in the top 50.
http://www.census.gov/newsroom/releases/archives/population/cb12-55.html
Some interesting stats in there. I didn't know that the Tri-Cities in Washington was growing so fast. I also found strange that Dallas County, IA is among the top 10 fastest growing counties when Iowa as a state is growing very slowly. Most of that growth into Dallas County is likely just suburban growth coming out of Des Moines and Polk County. Having Orleans and St. Bernard Parishes among the fastest growing counties is certainly a change, although that is mostly just repopulation after Hurricane Katrina. It will be interesting to see how long that growth continues and whether they ever regain their pre-Katrina population. Also, it's interesting to see how some areas like Las Vegas have really been hurt by the poor economy and others like in Texas have been able to continue growth unabated. The energy boom in North Dakota is obviously showing up in the population figures as well.
The Dallas County, IA situation is similar to DeSoto County, MS. The state itself isn't growing much, but they're getting a lot of growth from Memphis.
As for New Orleans, it's really hard to say. It's a great city to have fun in and they get a lot of conventions, crime is very rampant and the city is in danger of sinking into the gulf. It's hard to come back from that.