Eek.<p>I think, and I stress that this is wrought of my own unprofessional feelings, but I think that in the early days of rich consumer UI (pre-2004 lets say), that rounded corners, gradients and shadows did some great things to design, because they created affordances so that people knew, for instance, that a button was a button. It stood out against the other website clutter and cruft.<p>But we've sort of moved on. I'm reminded of a Doisneau quote (famous photographer, 1912-1994):<p>> "Nowadays people's visual imagination is so much more sophisticated, so much more developed, particularly in young people, that now you can make an image which just slightly suggests something, they can make of it what they will."<p>Nowaday's peoples visual expectations of what they might find on a website or app are much better, and you don't need to "point out" as much stuff. In other words I think users "got better". At the same time, we seem to see a real slimming of other visual distractions, so buttons don't <i>need</i> to be pointed-out as much.<p>This is the essence of Flat-UI in my opinion, that if you remove enough cruft, then afterwards you can remove <i>even more cruft</i> since your buttons and menus will no longer need to stand out from other stuff with gradients/shadows/rounded corners, and users are more attending to looking for them and expecting them anyway.<p>And I think, in light of all that, Yahoo sort of dropped the ball here. They didn't remove the cruft! Distractions distractions distractions.