>  in other words, all the widgets (menus included) of an app turned into
margins when mouse's /not/ over those widgets.


yes!! i agree 100%
last night i couldn't sleep  for a while, so i tried to imagine acme as a
whole screen ui, w/o any taglines, ctrl-boxes, and sliders... however, i ran
into problems soon... made some sketches, but ended up with acknowledging a
very clever acme design.
Nevertheless, it would be elegant if all the widgets were invisible, in the
way dexen proposed.. i hope to see it implemented soon ;-)
++pac