I successfully installed GNOME 3 and GNOME Shell from the Launchpad PPA on my fully updated Natty test system. However, nothing I tried could get it to actually run.

If I selected it in the startup options, I got a plain light blue screen with absolutely nothing on it.

If I tried to start it using gnome-shell --replace, I got:

gnome-shell --replace &
[2] 3251
tim@nattytest:/usr/lib$ Traceback (most recent call last):
  File "/usr/bin/gnome-shell", line 705, in <module>
    normal_exit = run_shell()
  File "/usr/bin/gnome-shell", line 293, in run_shell
    if shell is None:
UnboundLocalError: local variable 'shell' referenced before assignment
/usr/bin/compiz (core) - Error: Screen 0 on display ":0.0" already has a window manager; try using the --replace option to replace the current window manager.

[2]+  Exit 1                  gnome-shell --replace

I also tried preceding that with metacity --replace, as suggested at ubuntuforums.com. But, I got the same failure.

I also linked /usr/lib/libmozjs.so to /usr/lib/xulrunner-2.0b12/libmozjs.so, which did not help either. No matter what I try, I get the same error messages.