IMHO Ballmer was never supposed to be CEO, except maybe on a temporary basis. MS needs a technologist at the helm.
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.
From Wikipedia:
According to web analytics data generated by W3Schools, as of June 2011, Windows XP is the most widely used operating system for accessing the Internet in the world with a 39.7% market share, having peaked at 76.1% in January 2007.