The last example in http://doc.trolltech.com/4.6-snapshot/animation-overview.html does not work. According to http://labs.trolltech.com/blogs/2009/07/23/qstatemachines-a-state-too/ , the fix is:

Replace "machine->rootState()" with "machine"

As a side note, maybe using addDefaultAnimation would make this example slightly cleaner? I.e, use:

machine->addDefaultAnimation(new QPropertyAnimation(button, "geometry"));

instead of

transition1->addAnimation(new QPropertyAnimation(button, "geometry"));
transition2->addAnimation(new QPropertyAnimation(button, "geometry"));