Like others, I only created an account to say how much I hate the new UI. Please, Piriform, don't follow this hideous flat trend.
Going too far with 3D effects and transparency is one thing but a completely flat style (i.e. removing shadows and gradients like Windows 8 did) means you need stark color contrasts and huge borders (as well as huge fonts in the Settings interface) to make things out, to know what's clickable or what's on top. I don't see how that, added to the extra-sharp edges and corners, make Windows 8 "calmer" or "easier on the eyes".
And flat pictograms aren't by nature any "more simple to understand, universal and obvious" than other icons. They're just commonly used and accepted stylized forms, which has nothing to do with flatness. If you're not familiar with some of them, the lack of shadows and gradients is actually one less tool to convey what they're supposed to represent.
This at least I can agree with. I didn't spend all this time reskinning Windows 8 (preinstalled on my laptop) with 3rd party themes and tools to be be stuck with this ugly UI anyway.