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…
(Everything in that screenshot is a button. That's how Metro works)