Microsoft seems to be the biggest current proponent of flat design, and I must say it's not so great for usability. When I see this: http://www.istartedsomething.com/wp-content/uploads/2011/09/... I have no idea what is and is not a button. I suppose it's all a button. But there are zero affordances in this UI. This is now finding its way to Microsoft's websites. On outlook, I can't quickly find the buttons to do key…
Granted, the visual clues from bevels, drop shadows and whatnot had the bonus of instant familiarity to people not accustomed to GUIs. Nevertheless this might have been a sort of a crutch and nowadays people even if they expect the computer to emulate their home appliances, the appliances themselves have less and less buttons and levers and more and more touchscreens or at least touch-buttons.