In a previous post, I was complaining how bad Gnome 3 was. Since I have installed a real dock: docky, it is now much more usable. I can easily switch / launch applications without an annoying full screen change.
In addition I found out that it had a good desktop search (tracker). The ALT+F2 also does some sort of completion, too bad it can not use tracker here as well.
So it looks like Gnome 3 + gnome-tweak-tool + docky makes a reasonably good desktop. XFCE does not really fit the bill for me: bad handling of sound, bad default applications, not so good integration with gnome application notifications.
Now if only I found a way to change this ugly big white scrollbar...