We've looked at GPU accelleration for Rosetta in the past, and the conclusion by the people who were playing around with it was that - given how Rosetta does things - there isn't much benefit for GPU acceleration for most of the normal Rosetta protocols. As such, most of Rosetta does not take advantage of the GPU. That said, there are a few sub-protocols which have the facility for GPU accelleration, but unfortunately to enable this you need a special compilation, so most people don't bother.