I guess with games there is already temporal anti-aliasing (TAA), so that would be an effective denoising technique if one was using noisy ray/path tracing.
That's definitely popular for effects that use ray casting. At SIGGRAPH and GDC over the past couple years, a good fraction of the graphics presentations I went to ended with "and then we added TAA because we could only afford a handful of samples per pixel per frame".
