Metro IS the problem
"the problem isn't the tablet-friendly Metro layer per se. It's the severe disruption to the everyday experience caused by integrating Metro front and centre."
I think the author doesn't get it. The change from start menu to (Metro) start screen is hardly the problem, because in the end people may complain but eventually will adapt to the changes. Its not even a problem that MS pushes this down our throats because in all fairness; MS has a tendency to "stick with their ideas" when they got something between their ears. You'll have a hard time convincing them of their errors. It has happened before and believe it or not: sometimes this actually turned out for the better.
No, being a very happy Metro user myself (on my Windows Phone, which use I really enjoy) I say Metro IS the problem when it comes to Windows 8. Especially for businesses, though I think also for end-users.
Put differently: To go from a Windowed "multitasking" environment to a one-program-per-screen environment is simply preposterous. And the worse part is that MS belief in this concept seems to reach the edge of fanaticism; even in the trusty desktop app we are no longer allowed to see what other programs are up to: No more taskbars in icons, no more quick program previews by hovering your mouse over the icon; all of that which was Aero will also be taken away. The desktop, like Metro, will mean "concentrate on the current program and don't bother with the rest". Just like the Metro doctrine.
THAT is your main problem. Metro basically means turning your back on everything which made Windows the specific environment it is today (Windows 7). This isn't about people needing to adapt, its about people who are no longer able to do the things they need to do in an (fairly) easy manner.
Not to mention that Metro is by far ready for desktop usage. Music player? Has no volume control. Picture viewer? Can't even touch the ease of use one gets with IrfanView. All flakey stuff which MS probably hopes to get replaced with 3rd party programs.