At my last job, I had a few very productive chances to work with the folks responsible for IT design, from web pages and online "assets" like Flash presentations to new applications or interfaces on old ones. Every time I got to work with these guys, I came away more impressed by the care and skill they put into their work, and it got me to wondering about the rules and theory of interface design.
From browsing various design websites and blogs, I know it's a rich field - as it should be, given the billions of dollars in R&D and trillions of dollars in products at stake. Proof of this is this fascinating a post on a Microsoft Office interface-designer's blog about "Fitts' law," which, as applied to IT interfaces, governs the location and size of icons.
Among other things, the post implicitly demonstrates why the Mac OS X "Exposé" feature - which lets you use the four corners or the screen to do certain preset tasks, like view the desktop by moving every open window out of the way or launch the screensaver - is so effective. I love Exposé, and use it probably once every ten minutes. As part of a broader set of of Mac-specific features, Exposé shows that Apple (and its third-party developers) did their thinking before the designing and making. As they say, "it just works."