With the fantastic "Toy Story 3," Pixar has yet again set out to use its expertise to solve a huge computing problem, one that by necessity takes the place of what otherwise would be an impossible animation task. In the case of the new film, the challenge was to figure out how to craft a very complex scene in which the movie's heroes--Woody, Buzz Lightyear, Jessie, Hamm, Rex, and so on--have to navigate their way down a conveyor belt inside a trash processing facility, on which thousands and thousands of small pieces of ground-up garbage are moving toward a giant blast furnace.
To watch the scene is to believe it's live action. The garbage glints in what little light there is. You can see detail on many of the pieces, and there are thousands and thousands of them. It's a little gross, but it's an incredibly intricate and complex sequence.
It also includes a brief description of the technical aspect of other Pixar movies such as "Up". A wonderful article to read, even if you don't care or understand about the technology behind all this, just to appreciate the amazing effort that was put into these movies.