I love the Command model, with the CanExecute handler. No more fucking about with enabling menu items, toolbar buttons, keyboard shortcuts and all that nonsense. One check in one place and it's magically picked up by everything.
I created a DialogCommands class with OK and Cancel commands in it, and got them to automatically wire themselves up to Enter and Escape.
So much better than any other UI framework I've ever used.
EDITED: 24 Dec 2008 14:05 by RENDLE