While looking out to solve another problem, I've disturbed the opening of Unity session by altering (suppresssing) GConf (as suggested somewhere between, Ubuntu doc, forums and Ask Ubuntu) - now Unity opens on my wallpaper, with a top command bar but without panel or launcher, and with mouse arrow replaced by a (Linux) cross ; when I open a terminal, it opens on the desktop directory, and I have to run a unity --replace
command to get Unity fully up and running.
There must be a small piece of code somewhere that provokes this mess, but I have no idea about where to look or what to look for.