The Gnome Shell 3.6 builds are available for Ubuntu 12.10; but if you want to install the unstable builds of Gnome Shell 3.7 to test it out on your computer, then these commands will install it.
sudo add-apt-repository ppa:gnome3-team/gnome3 #The GNOME3 team PPA
sudo add-apt-repository ppa:gnome3-team/gnome3-staging #The GNOME3 staging PPA
Once these commands have completed; update the software repository information.
sudo apt-get update
if you have already installed a version of Gnome Shell, then you may type this command to upgrade to the latest version.
sudo apt-get upgrade
Or you may run this command to install it from the repositories.
sudo apt-get install gnome-shell
The 3.7 release of the Gnome desktop might not be very stable yet, but it would be worth trying out to have a look at the new features they have put into the Gnome desktop interface. Gnome Shell now has access to online services that you have granted Gnome access to and this means that your Google or Twitter account could be searchable as well as the local files when you are looking for something. This is not the same as the botnet system in the Unity desktop that sends everything you search for to Amazon. That is why it is better to not use Unity. Gnome Shell is a good desktop, but MATE is a far better and more attractive choice. The re is an Ubuntu respin that uses the Ubuntu desktop. That would be a better option for those of us who do not trust Unity. And there are many good themes for MATE that make it a cut above the rest: http://www.securitronlinux.com/bejiitaswrath/lovely-gtk-themes-for-the-linux-mint-mate-desktop/.