what the heck is this "uncanny valley" everyone speaks of? it's like me saying "iirc" you too would be confused as well as many don't understand what it means.

Here ya go, Daft. This is the page Kia was talking about:

http://en.wikipedia.org/wiki/Uncanny_valley

That page explains the theory, but here's the gist of it:

"The uncanny valley is a hypothesis regarding the field of robotics. The theory holds that when robots and other facsimiles of humans look and act almost like actual humans, it causes a response of revulsion among human observers. The "valley" in question is a dip in a proposed graph of the positivity of human reaction as a function of a robot's lifelikeness."

It further explains:

"Mori's hypothesis states that as a robot is made more humanlike in its appearance and motion, the emotional response from a human being to the robot will become increasingly positive and empathic, until a point is reached beyond which the response quickly becomes that of strong revulsion. However, as the appearance and motion continue to become less distinguishable from a human being, the emotional response becomes positive once more and approaches human-to-human empathy levels.

This area of repulsive response aroused by a robot with appearance and motion between a "barely human" and "fully human" entity is called the uncanny valley. The name captures the idea that a robot which is "almost human" will seem overly "strange" to a human being and thus will fail to evoke the empathic response required for productive human-robot interaction."

So basically apply that theory to the CGI in TRON: Legacy and that's what everybody is talking about.

To put it simpler: It is the creepy feeling that some people get when they see young Flynn saying "we're always on the same team" in trailer 3. The effect is less in the Clu's "I'm not your father" and much less in "Kevin Flynn, where are you now!".