I have a wonderful New answer for you! (I joined just so I could share this..) I bought a new card recently (a Quadro K4000) and I remembered that 'GPU' renderers required cards like this (which I had put to the back of my mind for years as my card at that time was a measly Quadro FX 4600)
So I started to look into them again, and VOILA' At Last ----> In addition to the 'photorealistic iRay and VrayRT there is a new OPTION for people who want to render FAST as HELL without worrying about total accuracy (or as a Carton look or CGI'Mation etc. It's called: FURRYBALL and it works with all 3D Packages, it has 2 renderers 'Normal mode' where you can do whatever you want. Unlimited options and looks possible. Then theres Raytrace mode for total accuracy- It's the first CGI thing I have gotten this excited about in a long time (well that and my QUADRO KEPLER4000 ;~) Here's the info page, http://furryball.aaa-studio.eu/
As you can see from my Animated work here:
I try for a more 'Illustrated' feel in my CGI and don't need physical accuracy! I need freedom and FAST FAST FAST renders!! Scenes like these go from 3-12 minutes a frame (rendering on 12 CPU cores) to more like,... 12-20 SECONDS! (or faster...) Rendering on CPU+GPU (I also wanted to mention that, You can control what does what, but the GPU renderer's in general will male use of every GPU AND CPU to get the job done!! The world begins anew today for smaller animation studios and Freelance Character Animators Like Me!
I have found it helps to offload PhysX to the CPU to leave more room on the GPU for interactivity (in Nvidia control panel, 3D Settings / Set PhysX Configuration (Defaults to Auto, switching to CPU can help a GPU render)
ENJOY!