There is a difference between flat and (more) usable. While I strongly question the necessity of shadows and gradients as a means to convey structure, they more

There is a difference between flat and (more) usable. While I strongly question the necessity of shadows and gradients as a means to convey structure, they more often that not help convey functionality to the non-rational part of the user's brain. Particularly the github example comes to mind: it may be a blue circle, but only with a smooth blueish shadow does it convey the meaning of an LED that wants the user's attention. A blanket removal of usually carefully designed interfaces comes close to art vandalism :) It might do good in some cases, but destroys the hard work put in many others.