The two main projects that I can think of were:
1) Younes Manton, GSoC project. g3dvl, already mentioned in this thread
2) Robert Rudd @ MIT. Another GSoC project that attempted H.264 decode via GLSL shaders using the ffmpeg/libav framework as a starting base. He got some stuff working, but didn't finish the project. Someone forked his code and at least got it to compile:
https://github.com/kasbah/gsoc.
Give it a few weeks, and I'll be sending my initial VP8 OpenCL implementation to the WebM mailing list to live in a sandbox while I continue work on it post-graduation. It's functional, but much slower than CPU-only decoding at the moment. It does at least produce correct output... in its own good time.
Once its in the sandbox and my thesis is finished up, I wouldn't object to anyone helping me out with getting the performance up to speed.