That is correct. Building dept. can only inforce codes ineffect at time of permit application. That is why there is always a rush of permits before Impact fees are put into place. It may take a year to start the job but they beat the new fees. Inspections are a PITA at code change time. 2005 NEC went into effect in Florida 01/01/07. Permits issued before that date are inspected to the 2002 code. Some of the houses I am inspecting now were issued in 2005. VERY large and expencive homes.
It's not so much "when the 2008 comes out" as it is when the lawmakers for the area that the "job" is in, when the lawmakers say that the 2008 NEC goes into effect. This "when" is different all over the country.
I just received a note a few days ago that Michigan will adopt the 2005 NEC 11/23/2007.
You'll need to find out your details from your local AHJ (authority having jurisdiction).