More thoughts on Global Illumination

As I sit and wait for another really long render, I am looking for things to keep me productive. Not sure if the blog qualifies, but what the heck.What to do when waiting for a render. General  summary: Keep busy.
My thought on Global Illumination is "Wow that looks nice!" Followed by "Good lord, it is only how far along?" as I wait for a full res, high quality render. While the big studios have just recently gotten to the point where they are using GI most of the time, this is made possible by two things the average Jane like me doesn't have. One is a gigantic renderfarm (Pixar ramped up to 12,500 cores for Cars 2), and the other is proprietary software that makes things go a bit faster which they do not always share with me and you.

Tip of the Day:
On another track, as a professor I often see ambient occlusion used incorrectly. So here's the correct and incorrect ways to implement it. Ambient occlusion is often multiplied with the beauty pass in the composite. This is incorrect. It actually should only affect the ambient contribution  or else you will end up with overdone occlusion in the areas of direct light.
INCORRECT:

Occlusion multiplied by the entire render leads to too much occlusion. Notice the dark shadow in front of the clown.

CORRECT:

In this example using render passes, you need three passes: Occlusion, ambient only, and direct light only. Occlusion should affect ambient only, then be added to the direct light for better results.