Given that the userbase of personal computing devices (not necessarily PCs or laptops) is still growing and will be for a while, the point at which Microsoft offers an operating system that isn't the "best selling version ever" will be a disaster for the company.

Truth is: it's very difficult to buy large classes of equipment without buying Windows due to OEM relationships, same as it's ever been. I've got Win7 that came with my current Thinkpad, but I've booted it maybe two or three times, getting as far as logging in. Otherwise it's strictly been Debian. Haven't even bothered setting up Win7 under VirtualBox yet.

I don't know that Ballmer's been a disaster for Microsoft, or if it's just running down the Christensen "innovator's dilemma" curve, but the company's best days are behind it.

In ten years I see it as a legacy provider of business servers to late-adopting companies, ossified industrial giants, some government sectors, and, principally, gaming and entertainment. Possibly merged with Sony.