Yes, GPUs are becoming increasingly flexible, but they are still limited by CPU-GPU bottleneck, GPU memory (which for the most part has been limited to 2 GB per card), really poor branching performance and limited ability to modify data in any other way than 1:1 correspondence. They are first and foremost designed to pump out polygons at high fill rates, which is fine unless you want to do some untraditional rendering or computation. :) Again, CUDA and OpenCL are paving the way for a new path, but I still think we should be using general purpose silicon underneath it instead of hardware designed to to do things like MSAA, interpolation, triangle setup, etc.