D3D11 compute shaders have definitely been used in shipping games. For most part they are only used for purely graphical features, like full-screen effects and times deferred rendering (used in Battlefield 3). The reason for this is that graphics is typically the easiest and most obvious use-case for compute, since graphics operations are generally well-suited to the massively-parallel model used on GPU's. Graphics operations also don't have to be synchronized with the CPU and read back to system memory, which is expensive on a typical PC architecture. Another reason for this is that PC games still need to target sub-DX11 GPU's, so it probably doesn't make sense to require DX11 functionality for gameplay-centric features.

As for CUDA, several games have made use of PhysX to run various cosmetic physics simulations on the GPU. RAGE also supported using CUDA for run-time transcoding of texture data.

I'm not an expert on OpenCL, but I would suspect that it's not getting much use in games. From what I understand it currently has a lot of issues with regards to getting a OpenCL program to run consistently on a wide range of hardware/drivers.

You can easily get away with DX10 as a minimum requirement today, that will at least give you compute shaders, though limited.

One of the reasons I suspect that graphical niceties have been the primary use is consoles, the gameplay needs to run on consoles too, which obviously don't have Compute Shaders. So sticking with a few graphical extras on the PC version doesn't hinder anything.

Still, I wonder what you could use it for, besides some physics acceleration ala PhysX. Regardless, I don't doubt we'll see DX11 cards as the new minimum, so compute shaders should be relevant to look into.