The Census Bureau has just released the latest county-based population estimates, with a reference date of July 1, 2006. You can access the data here:
So, if you know the components of your area's MSA and/or CSA, you can now calculate the population estimate for July, 2006. I'll start with Atlanta.
Atlanta Sandy Springs Marietta MSA 2000: 4,281,616 / 2006: 5,138,223
The Atlanta CSA adds the Gainesville, GA MSA, and the micropolitan areas of Cedartown, GA, LaGrange, GA, Thomaston, GA, and Valley, AL:
Atlanta Sandy Springs Gainesville CSA 2000: 4,583,958 / 2006: 5,478,667
As is readily apparent from the above numbers, the Atlanta MSA and CSA are continuing with relentless and astonishing growth so far this decade, with the CSA adding nearly 900,000 people in the last 6 years. The Census Bureau noted that, in the 2000 through 2006 period, Georgia had 14 of the nation's 100 fastest-growing counties, leading the nation in that number, and three of the top 10.