We've been making an open source GPGPU-based raytracer for the last couple of weeks, and it has become quite usable.
The project is up on github here: https://github.com/MadrMan/gpgpuraytrace (binaries can be found under downloads here: https://github.com/MadrMan/gpgpuraytrace/downloads)
The raytracer runs realtime at a small resolution on my ATI HD6870 (roughly 10fps)
We're using DirectCompute to do all the raytracing, and the raytracer is tweakable by editing the shaders in the shader folder.
The algorithm we're using to generate the landscape is currently not so great - there's still a lot to do. Any tips regarding performance are much appreciated.
Screenshots below or see http://imgur.com/a/ECPGb
