Stream Computing uses the GPU as a compute engine rather than strictly for graphics. If you have a problem set that maps to a GPU, it will absolutely scream when compared to a plain old CPU. If you look at the architecture of a GPU, it is a bunch of shaders, tens of them in most cases, each of which can crunch a lot of heavy sums, or at least certain types of heavy sum.
Regardless of whether you run Folding or not, a 30x increase is an incredible gain for the amount of cash it requires. Not to mention having a great gaming card on the side as a benefit! But as we all know… Folders don’t game.