Both of these were represented at GDC this year.  Jeremy Shopf presented a talk on Mixed Resolution Rendering, and the ambient occlusion technique presented in the talk Rendering Techniques in Gears of War 2 (available on the GDC Vault site) made use of both methods.  The ambient occlusion factors were rendered at a downsampled resolution. In addition, reprojection caching was used to reduce temporal aliasing.  This is the first use I have seen of reprojection caching in a shipping game.

In my previous blog post, I was skeptical of reprojection approaches, since it seemed to me that as an optimization method they did not address the worst case (where the camera angle changes abruptly).  Using such approaches to improve quality instead (as Epic did) makes more sense.

Lots of OpenGL and OpenCL stuff is available on the Khronos web site,  and Jeremy Shopf and Jim Tilander have their respective slides up as well. A Google Search for ‘”GDC 2009″ slides’ should turn up more as time goes by.