Windows 8 interface
I would suggest that the main problem with Windows 8, and any other touch-screen-style OSs, is the focus on apps.
Users in a workplace are document-centric, not app-centric. They look for "this invoice" or "that customer proposal" or the other "minutes from that boring meeting we had with the lawyers several months ago that we'd completely forgotten about but is suddenly the most important document in the business."
They don't care (sorry, shouldn't care) which app a particular document opens in. Users don't open Word and then go searching for the document they need. They search for the document and it opens in whichever app is the default.
I do see that Skype might be an exception but for the whole OS to focus on apps is misguided, at least in a workplace.