Sure it's an exaggeration. The uncanny valley is a visceral biological reaction in parts of our brains that have spent millions of years become very finely tune

Sure it's an exaggeration. The uncanny valley is a visceral biological reaction in parts of our brains that have spent millions of years become very finely tuned to identifying human beings. We have no such location for user interface. That said, I think there is still something to be said for the concept. If you are trying to mimic something, and get it 99% of the way there, that last 1% _can_ be source of frustration. (Jeff goes on to say because it _can_ be, it therefore is a bad idea, and you shouldn't do it. This is a poorly supported conclusion.) For example, stupid cnnsi.com has a "main window" that has some things at the bottom that look, feel, and act like links. Yet I cannot middle click them to open them in a new tab. This annoys the bejesus out of me. Another example is desktop-emulating applications who don't have a fully-functional right-click menu like I'd expect. By emulating other things, you put expectations into your user's mind about what sorts of functionality it should have. In this respect, it is analogous to the uncanny valley. The mimicry alone has created expectations that can cause frustration. But, that doesn't mean, that mimic'ing is inherently wrong or bad. It just means you have to do it right. You have to meet those user's new expectations.