This article by sci-fi author Neal Stephenson, is a very interesting and insightful read on the world of user interfaces. Though a bit dated (covers up through roughly 1999), it is still worth the few hours it will take you to read it, and it is available for free on the internet.

Stephenson on the idea that one could sell an OS to a consumer:

Even those few who actually understood what a computer operating system was were apt to think of it as a fantastically arcane engineering prodigy, like a breeder reactor or a U-2 spy plane, and not something that could ever be (in the parlance of high-tech) “productized.”