Have you ever heard of the "uncanny valley." It's a pop science theory which holds that, as robots and digitally created beings are rendered in increasingly realistic ways, we humans become increasingly repulsed by their appearance. The hit TV series "30 Rock" actually offers one of the most layman-friendly explanations available, after Tracy Jordan (Tracy Morgan) asks Frank (Judah Friedlander) to explain the concept "in 'Star Wars'":

Frank: "All right." [holds up line graph] "We like R2-D2. And C-3P0."
Tracy: "They're nice."
Frank: "And up here we have a real person." [points to end of graph] "Like Han Solo."
Tracy: "He acts like he doesn't care, but he does."
Frank: "But down here we have a CGI Stormtrooper, or Tom Hanks in 'The Polar Express'." [indicates lowest point on chart]
Tracy: "I'm scared! Get me outta there!" Read more...