It's interesting that only 7 years ago you probably wouldn't have be able to sit me in front of a Windows machine without resistance or at least some complaining. Since then I turned out to be a frequent defender of Microsoft in my surroundings and I'm considering ditching my Apple ecosystem for Windows 8 (esp. because of Surface and Windows Phone 8).
But the real problem, as have stated other, is OEM software and 3rd-party-apps. It takes effort to maintain your system (although not much, at least in my opinion, but you have to pay attention to, for example, what is installed along the way). I usually have none of the problems my peers or friends have (with Windows) and if you look at their machine, you'll see why. Almost every time I visit my father, there is a new (worthless) toolbar installed.