Berkeley philosophy professor Alva Noe has a pretty fascinating take on the Uncanny Valley as caused by 3D computer-generated movies like The Polar Express and Tintin (which I talked about recently). If understand him right, he's arguing that the feeling of uncanniness happens when CGI simulations of people are incorporated into a movie, which we watch passively. This confuses our expectations, because cartoons usually demand a level of interactive imaginativeness in our viewing:

Cartoons don't give us glimpses of worlds, they give us worlds to play in and toys to play with. Live-action movies, in contrast, don't give us opportunities to play; they give us access to hidden worlds... the uncanny valley yawns [when animators]... get confused about what kinds of stories they are telling: Are they inviting audiences to play, or giving them an opportunity to watch? [emph. mine]

Read it all here. I think Noe's theory also explains why the Uncanny Valley effect doesn't seem to happen as much in 3D virtual worlds like Second Life -- while human-like avatars should tweak our sense of the uncanny, the fact that we're interactively participating in the simulation, with the knowledge that a real human is at a keyboard, operating each avatar, keeps us away from the Valley.

Hat tip: Andrew Sullivan. Noe, by the way, gave a great and accessible Google talk about consciousness which goes down like a smooth bourbon: