Unity has come a long way and still there are users who prefer the vintage Gnome experience without many bells and whistles. While the earlier Ubuntu versions came with gnome-session-fallback package, Vivid Vervet gets a change in the name of the classic desktop. To install, run:
$ sudo apt-get update $ sudo apt-get install gnome-session-flashback
Now you have two flashback sessions installed – Gnome Compiz Flashback and Gnome Metacity Flashback. Logout and select the classic desktop you prefer and login back.