Well Derek Smart said he will not support Cg. I know he is no carmark or sweeny. But he is a developer...
It works. The problem I see goes back to the whole Glide vs DX debate. As far as I can see, Cg is not standardized. In fact, some of the effects which should work on an ATI board, do not. In fact, some flat out crash it.
As such, I have my doubts as to whether any dev is going to waste their time using Cg to put in effects which only work on nVidia boards. Its bad enough that we (well, me personally) have exclusion code specifically geared toward making things work on ATI boards. Why would I want to add another layer of complexity to my code base.
For that, I'm probably not going to touch Cg for anything - other than prototyping. Its cool for that.
However, it might be really nice if developers start to really adopt the NV30 for games which would release about 14 months after the NV30 release. That would be a really good win for nV - it took them years for Transform and Lighting and about 2 years for shaders.
NV only had 53% of the graphics market. Why code for only 1/2 the market? If any developer did that they will stand a chance to lose 1/2 of their projected income. Do you think that will happen?
In all likelyhood the extra vertex shaders power will probably not be used as there is no need to write something that complicated. In fact there was a long thread over at B3D about this. I will see if I can find it for ya