Although I mostly don't mind the flattening of ios, I think this would be terrible on the full OSX, at least the way this artist has depicted it. 3d information is actually really useful when you have multiple windows all piled up and tiled together. And interestingly, his mockup images all show single apps at once... In real life of course, many people multitask.... A fully flat approach like this wouldn't be very conductive to multitasking in a visual sense I think. Keeping track of window focus, etc. Might be a challenge when there's tons of stuff open at once. I don't inherently mind some flattening, etc., but there might be an impact on functionality. Of course, Apple does often make trade-offs where form takes precedence over functionality... :/