Can someone give me a run-down on the utility or otherwise of using NVIDIA's parallel nsight (in Visual Studio) for debugging OpenGL 3.3/4.2 + shaders? Is this possible? Is it desirable?

If it is possible, what configuration makes it possible? Do I need two cards in one machine, two machines?

Do ATI have a similar feature?

I've found debugging my OpenGL shaders to be hell, and I've tried other OpenGL debuggers, that seem not to work correctly or at all.