This is a great book, telling you things that you know in a way that makes you think that you didn't actually know it. And this time you don't ignore it.
A must read for a web developer!
but it looks to some extend outdated (I read the II edition - 2006)
In any case Nielsen remains the best one on this topic.
It's all about design. Knuth focuses on web design, but the bottom line is in Norman's book: every thing shall be designed in such a way that the USER don't need to THINK about what's going to happen when the THING is going to be used.
A good manual for software developers who do aren't keen on usability issues.