gpu video encode does not look bad, there are tons of videos encoded using the gpu in YouTube. in fact every camera in the market encode the footage using a dedicated chip in real time, not a general purpose X86 GPU.
the 3d engines are not prepared for GPU rendering yet, they just render using open gl, but is moving fast. Cinema 4d is going to add the amd render so we will see in a few months.
Maybe "look bad" was the wrong term, but they definitely don't look on par with what CPUs deliver.