can now render with Nvidia mental ray iRay, on a GPU. This is a photo realistic and physically right and it takes hours to render.
You can see the picture of the room that 8 cores, 16 threads from two quad core Nehalem’s are rendering for hours. You have a light that comes outside, semi reflective floor, reflecting glass table and this scene is super complicated to render.
On two Fermi GPU who have enough precision, they can show the same preview in a few seconds. The actual rendering still takes a long time, but most likely it will be faster than on GPUs.
They also showed that with 32 Fermi processors, you render the same scene via Cloud and stream it to your notebook, but this is something that will come in the future. Real-time interactive ray tracing tool that will definitely help a lot to architects around the world.