That's it. I want to have terminal windows to be (half-) transparent in Unity 2d without wasting too much resources.
This question has arisen after an update from Ubuntu 11.04 to 11.10, after which I was happy to find, that I can switch from Unity 3d back to Unity 2d.
I have tried to use gconf-editor, but haven't find anything useful there (only a few entries about unity-2d in desktop-->unity-2d, which doesn't seem to be relevant).