FlatUI is making it impossible to distinguish between buttons, tags, labels and tabs. Skeuomorphism, correctly derided in its cartoonish, Mac Calendar form, has come to mean having any depth in a UI. Sane-looking buttons? Skeuomorphic! Using an inset for an aside? Skeuomorphic! Icons? Skeuomorphic! Mouse pointer? Skeuomorphic!
It reminds me of the way the the Bauhaus guys would yell "Bourgeois!" at one another's designs until all they were left with were unlivable, white cubes: