I'm going to repeat a pair of recommendations that I'd posted some time back, but which accidentally got deleted. They are not specifically about OS programming; however, anyopne who is designing an OS would do well to read them both.
The Design of Everyday Things by
Donald A. Norman. I'm going to be very clear and blunt on this subject:
if you haven't read this book, you have no business designing anything which any other human being will need to use. Period.
While not specifically about computers, this book goes a long way in explaining the way people intereact with the world around them (the original title was
The Psychology of Everyday Things), and provides a basic overview of user design which is universal. While brief, the section on computer UIs is wonderfully enlightening; the two concepts of the Gulf of Execution (the degree to which the set of possible actions is visible to a user) and the Gulf of Evaluation (the amount of feedback the user gets when an action is taken) goes a long way in explaining what it really means for a design to be 'user-friendly'.
The Humane Interface by
Jef Raskin. Whereas DOET is a general guide to useability, THI is a manifesto about how computer UIs can and should be redesigned, to the benefit of novices and masters alike. Raskin was the original design lead on the Macintosh, and left the project when he concluded it was getting to complex; this was the original 128K Mac, mind you. He later went on to design the Canon Cat, an obscure but widely lauded design which is considered by those who know of it to be a triumph of simplicity, and a superior system to many that came later. The book goes to great lengths to explain just why the systems currently in use never seem to live up to their potential. THI has some serious flaws - Raskin has a lot of trouble explaining some of his better ideas (a lot of people interpret the idea of type-and-select actions as championing CLIs over GUIs, which is not the case at all), and much of the book is stuffily academic in tone - but still quite valuable and inspiring.