What's the best/right way to configure GNOME/Unity so that hitting ALT + F4 will Power Off the system when no more windows are open? (pop up the Power-Off dialog).
(running Ubuntu 12.04.1)
No.There is no short-cut for Power-off. But you could add one.
Go to System Settings ----> Keyboard -----> Click on the shortcuts tab ----> Click on the + button.
Now enter some name of the shortcut and the command
Now you can apply whatever keyboard shortcut you want to it. Click on the word that says Disabled... when you click New accelerator... will be shown. Now you assign it to whatever keyboard shortcut you want to it (that is by pressing Alt + F4 when you see the word New accelerator...)