If he's messing around in Compiz, it's also possible that he's stumbled on some combination of visual effects which broke the compositing window manager. Try going into System -> Preferences -> Appearance -> Visual Effects, and select None. If you get your title bars back, then try turning visual effects back on and see if it resets things to a sane state.
Compiz still has some rough edges. I generally leave the visual effects disabled on machines I use for real work, since it tends to break the VNC client (among other annoyances).
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