/. has a an item titled User-centric GUI Design Explained to All with some great links. Primarily they're pointing to an article titled Usable GUI Design "showing that good user interfaces are not beyond the means of free and open software development: 'This article presents five key points of user interface design [...] that any software developer should be able to use.'"

It's particularly timely for me since my time is discussing usability and our applications designs daily.