You'll find a quickie exchange between Beyond3D and John Carmack right here. Carmack has made some changes to the DOOM 3 engine's abilities, adding more shader eye candy:
I did decide rather late in the development to go ahead and implement a nice, flexible vertex / fragment programs / Cg interface with our material system. This is strictly for the ARB2 path, but you can conditionally enable stages with fallbacks for older hardware. I made a couple demo examples, and the artists have gone and put them all over the place...
News source: Tech Report
