On my laptop I currently have Ubuntu 12.04. When I open a second window of a terminal and minimize it using the control button on top (with the - sign), it seems to disappear. Left clicking on the task bar icon simply shows the one that is active. Alt Tab idem ditto. (Middle click opens a new one, right click shows nothing useful).
In Openbox I simply rightclick on the Desktop to see all active programs, but in Ubunbu that only shows a useless menu (align icons and such).
Turns out you need to learn a new key combination: Command Key + w (or Windows Key + w) to see all active windows. (At least for now, don't hold your breath.)