@marmuta: alt-F4 is a feature of compiz, so it isn't available in unity-2d. Now, if only the unity launchers allowed you to minimize windows...
@Quang: If this happens, ctrl-alt-f1 should give you a tty session, ie a command prompt. From there you can login and try to kill the onboard keyboard with "killall onboard". ctrl-alt-f7 or -f8 then should take you back to your X session (you can log out of the tty session first if you want).
@marmuta: alt-F4 is a feature of compiz, so it isn't available in unity-2d. Now, if only the unity launchers allowed you to minimize windows...
@Quang: If this happens, ctrl-alt-f1 should give you a tty session, ie a command prompt. From there you can login and try to kill the onboard keyboard with "killall onboard". ctrl-alt-f7 or -f8 then should take you back to your X session (you can log out of the tty session first if you want).