BTW, isn't apt-get upgrade supposed to be discouraged? I must say I've never used in myself on my N900.
Install status-area-orientationlock-applet. This will add an entry to your system menu. Use it to lock your phone in landscape. Uninstall status-area-orientationlock-applet. Job done. If you want to lock in portrait, tough luck. But why on earth would you want to do that?