GNOME Shell is mind blowling user interface of the GNOME desktop enivornment that was started with version 3. GNOME shells replaces different software component from GNOME 2 and also replace GNOME panel.If you are running Ubuntu 11.10 Oneiric Ocelot GNOME 3 has been places by default However the desktop enivornment is unity by default which is running on GNOME 3.1.5. You can try GNOME shell just by installing it either from terminal or Ubuntu software center.
Installing GNOME shell on Ubuntu 11.10
Open terminal(CTRL+ALT+T) and type the following command
sudo apt-get install gnome-shell
Install from Ubuntu software center
Go to Ubuntu Software center and type Gnome shell and install the application. See below screenshot for more detail
Log out from your system and choosing Gnome while login back.
Screenshot of GNOME Shell