I think it's been said that the fastest-growing areas are the most Republican, so Democrats shouldn't invest in a presidential win there for some time.
I think it could vote for a Democratic governor in the middle of an unpopular Republican presidency, though. Sheheen did very well there for a Democrat in 2010.
That's true in many places though. Probably the fastest growing area in Georgia is the 80% Republican Forsyth County. Charleston and Columbia have potential to trend dem with their population growth. Its true that the larger counties in South Carolina mostly tend to be Republican, which is unique, but that's also the case with New Hampshire (more Republican at least)
Sorry, but South Carolina is not trending D and it's also inelastic.
It appears to be trending D as much as Georgia is, that is to say, not much. Here's the margins relative to the country (from 2000 to 2012)
SC: R+16 R+15 R+16 R+14
GA: R+12 R+14 R+12 R+12