Eric Raymond's The Luxury of Ignorance: An Open-Source Horror Story rant:

..."GUI tools and voluminous manuals are not enough. You have to think about what the actual user experiences when he or she sits down to do actual stuff, and you have to think about it from the user's point of view. The CUPS people, despite good intentions, have utterly failed at this. I'm going to anatomize this failure in detail, because there are lessons here that other open-source projects would do well to heed. The point of this essay is not, therefore, just to beat up on the CUPS people — it's also to beat up on every other open-source designer who does equally thoughtless things under the fond delusion that a slick-looking UI is a well-designed UI. Watch and learn..."

This should be required reading for every student of CS for their HCI class.

I had a wry smile to myself when I read this paragraph:

"If the designers were half-smart about UI issues (like, say, Windows programers) they'd probe the local network neighborhood and omit the impossible entries. If they were really smart (like, say, Mac programmers) they'd leave the impossible choices in but gray them out, signifying that if your system were configured a bit differently you really could print on a Windows machine, assuming you were unfortunate enough to own one."...

If nothing else read the final two paragaphs of Raymond' follow-up in The Luxury of Ignorance: Part Deux:

"It's been twenty years since the GNU Manifesto and nearly seven since The Cathedral and the Bazaar. I think it's time we stopped congratulating ourselves quite so much on our dedication to freedom and our ability to write technically superior code, and began more often to ask What are we doing to serve the real users? Good UI design, and doing the right thing by Aunt Tillie, ought to be a matter of gut-level pride of craftsmanship.

But if that's too abstract and idealistic for you, think of this. No matter how skilled you are, there are many times when you will be the end user. By learning to demand good UI from others, the time and sanity you save will ultimately be your own."