Nicolas Roard just pointed me at a nice article from 1996 on possible UI improvements that can be achieved by doing the opposite of currently accepted GUI rules.
E.g. it has this to say about consistency in GUIs:
Consistency is one of those principles that sounds like a great idea when you first come across it, but it is very difficult to apply the principle in any real situation where there is a wide array of conflicting things with which you can be consistent .
Definitely an article worth reading.
The basic advantage of consistency is the hope that learning will be reduced if objects with a similar function always look and behave the same. People will recognize applications more easily if they all have similar icons. Yet in the real world, people have no difficulty switching between ballpoint pens and fibertip pens even though they look somewhat different and have different controls. They are similar enough that they are both recognized as pens, whereas their varying appearances provide pleasure and clues to their slightly different functionality. It is the rich and fine-grained representation of objects in the real world that allows pens or books to have a wide variety of appearances and still be easily recognizable. As representations of objects in the computer interface become richer and more fine-grained, the need for complete consistency will drop.
Note that consistency is not symmetrical. Whereas we argue that objects with similar functions need not have consistent appearances or controls, it is still important objects with similar appearances have similar behavior and functions. Except as a joke, a pen that looks like a tennis shoe will not be very useful.