Recently, I picked up a spare 8GB USB thumb drive so that I could test out various distributions. I spent yesterday running Fedora 16 that way, to give gnome-shell a shake or two, since it was resisting my efforts to get it to run under 3D acceleration in VirtualBox.
It turns out that there's one detail I can't stand, and I'd especially not be able to stand if I were switching between gnome3 at home and MS Windows at work: they broke Alt+Tab by introducing Alt+Grave. With two browser windows and Rhythmbox open, I kept getting Rhythmbox instead of "the last used window". Also, the Alt+Tab switcher considers all workspaces, which defeats the point of them.
So the race for "what to do when Ubuntu 12.04 comes out" is down to Unity vs. KDE for me. (I've been sticking to LTS versions since I no longer particularly like fixing things and adapting to gratuitous changes every six months.)