[joshuak]

Interesting questions. I don't have the answers, but I can say that I can't imagine that Pixar would ever 'go all the way' to an 'unbiased' GI renderer.

Our entire function in the filmmaking business is to tell a story visually, and for that you need complete control and directability of the image. This is the opposite goal of unbiased renderers. Nevertheless more tools in the tool box is always good.

[berkut]

Unbiased actually isn't slow - Arnold has proved this - what's slow is using hundreds of bounces per path and bi-directional path tracing (like Maxwell, Indigo, LuxRender) which takes a lot longer.

Biased generally means it's interpolated with a point or irradiance cache.