During SIGGRAPH 2008 in Los Angeles NVIDIA is demonstrating a fully interactive GPU-based ray tracer. The demo is based purely on NVIDIA GPU technology, and according to NVIDIA the ray tracer shows linear scaling rendering of a complex, two-million polygon, anti-aliased automotive styling application.

At three bounces, performance is demonstrated at up to 30 frames per second (fps) at HD resolutions of 1920x1080 for an image-based lighting paint shader, ray traced shadows, and reflections and refractions running on four next-generation Quadro GPUs in an NVIDIA Quadro Plex 2100 D4 Visual Computing System (VCS). We've got some screenshots and information from the demo posted right here...