You might not think there's much to this, but good old Windows has had a profound influence on the development of computer technology, the modes of use we are all most familiar with and the progress of everything from graphics processing hardware to user interface design. While it's entirely reasonable to argue that their efforts were unoriginal among many other things, one thing that can't be denied is the ubiquity of windows. In fact, it's only really been in the last decade that there have been readily accessible alternatives for the majority of users. This ubiquity has been an important force, for good or ill, but some of the good ones have been great. Sometimes standardisation is important. It's not lost on me that standardisation, the practice of doing things the same way, is actually a driving force for innovation. It has a limit, there comes a point where the progress stagnates but standardisation has clear economic advantages that allow resources to be spent elsewhere on newer developments. It's not until developers begin hitting the constraints of a standard that the gains drop off.
The pseudo-memetic establishment of user paradigms is another distinct benefit. It's simply a matter of every computer user having encountered Windows; at school, at work and/or at home. It's common application breeds a familiarity that no other operating system was in a position to spread. Though you may argue that Windows is not the first or the best example of the GUI, it was the only one in a sufficiently dominant position to bring that interface to the world.
So for all it's issues, remember what Windows did for you.