Currently under heavy development, GNOME Shell is included in Ubuntu 10.10 Beta and it currently looks like this:
GNOME Shell in Ubuntu 10.10 Maverick Beta
The main feature that jumps into attention is the way of organizing and listing opened windows, just like the fast web access from Opera, for example. GNOME Shell also offers virtual desktops.
As you can see, GNOME Shell offers the user easy access to applications, places and devices, a way of searching applications or documents and recently accessed items.
You can switch between the Activities mode (where you can visualize all your opened applications and access more) and the normal way of working by clicking on the top-left Activities button, or just pointing your mouse cursor in the top-left corner.
Accessing your applications
If you want to quit GNOME Shell and return back to your usual GNOME desktop, open a terminal and type the following two commands:
compiz --replace &
gnome-panel restart &
If you don't have desktop effects enabled, use metacity --replace& instead of compiz --replace&.
To install GNOME Shell in Ubuntu 10.10 Maverick Beta, type in a terminal sudo apt-get install gnome-shell, and then to start it type gnome-shell --replace in order to replace your current window manager.
GNOME Shell definitely looks good and from a usability point of view, it really has a lot of potential, especially if we keep in mind that it's not finished yet, so more features will come.