Mac have a capability to specify two default buttons, one activated by return and other by spacebar. One clear example is when you press power button on mac. It gives you a dialog box with quiet a few buttons, in which it shutdown is default for return key and restart is default for spacebar key. Is it possible to achieve such effect in Qt?
Yes.
Use QPushButton. On the "default" button use setDefault and setAutoDefault() to make them appear as a default button.
http://doc.trolltech.com/4.7/qpushbutton.html#default-prop
To handle the escape key (and possibly even the return key), you must set the shortcuts for each button to associate them with a corresponding key. It's easy to do that using Qt Creator/Designer.