If you didn't know, the uncanny valley is a term coined in the seventies by a Japanese roboticist named Masahiro Mori. In short, the idea is that as a robot becomes more human-like in its design, it will cause an increasingly empathetic reaction, up until a certain point when it quickly becomes repulsion. Human beings add humanity and empathy to a huge range of things, inanimate or alive, but that ability begins to turn on itself when faced with a near-human entity.
It applies to many other fields - I'd argue that it's easier to humanize and empathize with this drawing of a wedge of brie
than this portrait, which is in a much more realistic style but "off" enough to repulse the viewer
Is that a good example? I'm not really sure since I picked a particularly creepy picture off deviant art....
But anyway this happens all the time in CG animation, if you watched the Polar Express or Beowulf you'll know exactly how this works. When that Final Fantasy movie came out, I was really excited because it was supposed to be the first movie where the line between live-action and computer-generated actors became blurred... looking at it now people definitely were getting ahead of themselves.
I started thinking about the uncanny valley again when I saw this video posted on Gizmodo - Image Metrics, a company specializing in facial animation, made this "interview" video using CGI. The valley still exists here, but it's narrower than most CG people I've ever seen.