You've heard me talk about simplicity quite a bit on this blog and in my presentations. It's really one of the most important things I stress to designers. The easier you can make your software to use, the happier your users will be.
For a bit of fun and some insight into the art of simplicity (and some enjoyable Microsoft bashing as well ;-), check out this great TED Talk featuring David Pogue, tech writer for the New York Times.
David Pogue: When it comes to tech, simplicity sells
(Thanks to Jane Griscti for the link)