I like Cg but it seems to be a long way behind GLSL/HLSL now - only supporting fragment & vertex shaders, for instance.
Is it still being developed or has it been given up - in which case is there no longer a way to write GPU-independent shaders?
Is Cg still being developed? Yes; NVIDIA continues to update Cg and keep it in sync with technology.
Does that make it not "dead"? That's a subjective question.