Re: "TIFKAM is perfectly usable, it just isn't the interface people are used to."
Metro is a UI designed down to the least common denominator, one designed for what a small screen touch only device is capable of (and I'd argue crap like magic corners is inherently bad design even there).
Not just different, it's an impoverished UI, hamstrung by it's assumptions:
1: that it has to look the same everywhere (a pure marketing requirement with no real reason to exist), where 'everywhere' leaks strongly into desktop mode (so even functional window chrome had to go)
2: that it has to behave identically everywhere, regardless of the quality or precision of your input devices
3: that fullscreen is always the 'right thing', whatever the hardware, whatever restrictions it causes
There's a more subtle assumption: that desktop=legacy mode. Legacy modes inevitably become 2nd class, with degraded support and allowed to rot before being dropped completely - at least in the minds of the managers and developers maintaining them... and Win8 desktop mode is showing signs of neglect, from the hastily crippled chrome and theming options to the astonishing bugginess of File Explorer to the almost random organisation of settings and on and on.
The real issue here remains the same, if I'm using an 'interface people (aren't) used to' there's no reason it should be a Microsoft interface. If users are increasingly using reduced function devices instead of PCs, Microsoft are screwed because traditional Windows doesn't work there.
Everything in Win8 has to train users to use the impoverished Metro UI that does work on new devices. Metro can't be allowed to work better on a PC than a tablet and desktop has to be subtly (and not so subtly) degraded to make Metro more attractive. It's cynical, desperate and failing.