Recently ATI's GPUs got support for Folding@home and it looks like NVIDIA's GPUs may soon get the same functionality:
FAH Project Director Vijay Pande talked to UK site Custom PC about the subject. He stated, "Our GPU code was originally developed for Nvidia GPUs, but recent ATi GPUs (X1900 class) have really pulled away from the previous generation of Nvidia GPUs. The G80 may change that and we are looking into it. Our code is written in Brook, so it's not limited in any way to ATi GPUs, although there may need to be code changes to achieve optimal performance on other hardware such as the G80."