I'll be quick on this one. Flat designs have inherent problems... 1) You can't tell if it is something you can click on like a button, or just a decoration (a box design) 2) The only way to differentiate between different boxes is only through color (since you are making everything flat). 3) Too many colors makes the screen confusing. So.... DON'T COPY WINDOWS 8! That thing is terrible terrible. You have no idea if it is just a decoration on the box or something you can interact with. BAD BAD design. The flattest you can go for buttons is one pixel to show depth (first tried on the old AmigaOS 4.0 I think). If you get rid of that depth, the design is trash. Look at Windows Phone 8. So many colors, so confusing, boxes the have colors that distracts, not knowing if you can interact with it or not. Requiring memorizing by shape (and the shapes are customizable). Windows Phone 8 flat design is NOT the way to do it. Too flat, and you ruin it... PERIOD. The best flat design is this... Buttons must show depth. There must be a differentiation between what is just text, and what is click(touch click) able. You can do this be either making them underlined, different color, etc like in web browsers, or provide some sort of marker (sometimes I see an arrow graphic, sometimes a box around it), but THERE MUST BE A MARKER. If not, people end up wasting so much time flipping through testing if it is a link or not. If it can be clicked on or not. So Ive has from now until iOS7 release to make sure this design does not make buttons purely flat. And add markers for interaction links. If he makes all the icons flat, you won't be able to tell if it is just a decoration or something you can click on. BAD BAD BAD. Similarly to the small screen size iPhone. They will pay dearly for keeping it small (until 2014). I hope the flat design does not follow in the same footsteps.