Attached Link: http://www.cs.ucy.ac.cy/ayia-napa06/presentations/ayianapa06per.ppt

They are much better in Photorealistic Renderman, which is what Pixar uses. I have no idea if they even exist in real ray tracers, like Mental Ray or vRay. Vue Studio has depth mapped shadows, I think they can be linked to single items.

Ray traced shadows are usually much easier to set up in an realistic environment. Pixar uses DM shadows a lot, but acording to some papers they published they use hundreds of lights in a single scene. 

Take a look at the linked PPT presentation - Pixar explains why they used Ray tracing in "Cars". Some nice details inside.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

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