Install Gnome3 Ubuntu 12.04

sudo apt-get install gnome-shell gnome-theme-standard gnome-tweak-tool gnome-contacts gnome-sushi dconf-tools

If you want the most extensions to work with Gnome Shell 3.4 I'll suggest PPA: http://ppa.launchpad.net/webupd8team/gnome3/ubuntu
As most of the extensions on gnome extensions site is not updated for Gnome Shell 3.4.


To uninstall Unity completely and run Gnome Shell only:

sudo apt-get purge appmenu-gtk appmenu-gtk3 appmenu-qt indicator-appmenu
 unity-lens-music unity-lens-applications unity-greeter unity-common unity-asset-pool unity-2d-launcher unity-2d libunity-misc4 libunity-2d-private0 gir1.2-unity-4.0 liboverlay-scrollbar-0.2-0 liboverlay-scrollbar3-0.2-0 overlay-scrollbar appmenu-gtk appmenu-gtk3 appmenu-qt indicator-appmenu compiz compiz-plugins-main-default libcompizconfig0

sudo apt-get purge lightdm
sudo apt-get install lightdm

Advisable: removing all local config files/folders/other local settings from "home" users. (I couldn't get Gnome Shell starting without doing this step at current state.

If you want to remove qt libs that are related to unity and other ubuntu applications:

sudo apt-get remove libqt4*

Note: if you have applications like vlc, ubuntuone and other qt depended. they will uninstalled as well.