The New York Times has an interesting article that previews the potential problems of Pixar (creators of Toy Story, Finding Nemo, Monsters, Inc. and others) as it approaches it's most ambitious film feat yet, animating human characters.
Pixar's upcoming film, The Incredibles, due out this November, will be their first film to focus on human characters. This brings to the company a new set of problems as human beings can recognize bad human emulation very easily (much more easily than that of toys or fish). The question is: will they blow it?
Based on this article, it appears that the company is taking the right approach and trying for mostly caricatured humans, which are much more compelling and believable because most people recognize them as representative.