thanks for these answers. Most of them makes sense. However, I am still convinced that transitions and states are not so closely related as it is enforced by QML. To me, states are more about logic, than about properties and assigned transitions. Thus the most important thing would not be transitions but onEnter, onLeave, onUpdate handlers and of course custom methods/actions. From these I could easily invoke any transition, which would more become a collection of Animations. This would nicely decouple the two things, and I could even reusing transitions for different states or objects or even refactor them into a separate file.
I have to try your key-press example. I guess, I'm slowly understanding what you are doing there. :-)
Powerful stuff, once you understood QML's potential...