pouët.net

Any thoughts about it? Anyone used it? How useful is it?

http://developer.nvidia.com/content/nvidia-nsight-visual-studio-edition

I doesn't do OpenGL performance counters or pipe line measurements (only API tracings)
Stick to ATI for opengl debugging / profiling
IMHO anyway

It's quite good - gives you a good overview of the activity on the GPU, of your renderframe and CPU-time spent too. I haven't tried it with CUDA or dx11, but probably even better then. I believe it has the ability to use two graphics-cards to do captures and playback on a running application as well.

Intel GPA and AMD Perfstudio are decent too.