It has been written again and again by many slashdotters, every time a stupid article came up about the supposed "downfall" of microsoft because of the Windows 8 failure and low sales. Ok tablets and smartphones are selling like shit, but most people still have their 5-year-old or so PCs/laptops around with windows XP or 7. Unless you're into gaming, there's just no need to do any fucking upgrade. Why go out and buy a new laptop with windows 8 or upgrade your existing windows to 8 ? Will it make browsing or receiving emails or writing a document or watching a video faster or better ? No. Will people stop using windows anytime soon? Again no. Why? Just look at the alternatives: OSX ? You need a Mac which is expensive. Linux? Nope, if you ask any casual user they wouldn't consider it for a bit. Hell, i'm into the IT industry and i have colleagues who are laughing at the idea of switching to a Linux OS because they want something that "just works". So no, windows ain't going away in the near future.
As for the enterprise, AD/Exchange are a big plus but i think the biggest advantage for Microsoft comes from Office and more specifically Excel. The only change that might hurt MS in the enterprise is the movement of big applications towards a web-based model where the user will only need a browser to use the application.