Examples of Nice CSS Styles
Thoughts on KDE This article makes some good points about usibility. On point boils down to: understand what the user wants to do 90% of the time and support that.
An example is an icon view that when it contains a number of picutures gets a button that says: display as slidshow.
There is also the suggestion that main windows be decorated with folders and panes that scroll out rather than making heavy use of dialogue boxes.