Isn't "Discoverable" another way of saying this? It can and does work. It's fun to find a feature or learn how to do something new.

Examples: iPhone. No manual (probably there is now). It's unbelievable, really. But, you have to admit it works!

Anti-example: fire extinguisher. No tricky interface, please.

One reason I didn't see mentioned is user level. Beginners want/need simple. Later, they want more power. How do you keep the advanced features out of the way of the new users? Hide them! Advanced users will find them when they are ready.