Please remove and blacklist gnome-shell
Binary package hint: gnome-shell
Due to the state of the GNOME3 stack in natty, we won't be able to upgrade gnome-shell to 2.91.x. In addition, due to libraries that have already changed, (Bug #685225 and Bug #677382), gnome-shell is currently broken. We also have the xulrunner-2.0 transition to consider. Due to all this, we believe it best to remove gnome-shell from natty.
The current plan is to get it built in the GNOME3 PPA and reintroduce when GNOME3 makes its way into Ubuntu.