From Techienote.com -
From last couple of months I am using UBUNTU 11.04 RC release. I am not die hard fan of GNOME but from the start of my Linux usage I am using GNOME over KDE. Now UBUNTU’s default desktop environment would be Unity, so I tried to make myself comfortable to this change and using unity from couple of months.
But I still found, I am more comfortable with GNOME rather than UNITY. I am writing this post for those who still want to use GNOME in UBUNTU 11.04.
For switching to the GNOME desktop environment you don’t need to install any extra package. You just need to select Ubuntu Classic Desktop while logging into UBUNTU 11.04 desktop. See the screen shot for better understanding.
1.) At Ubuntu 11.04 login screen, choose login to “ubuntu classic”.
2.) Right click on “main menu”, “global menu” at top left screen and uncheck “lock to panel”, then select to “remove from panel”
3.) Right click on top panel, choose “add to panel” and then add “menu bar”.
Now you’re in Ubuntu 11.04 with classic gnome desktop!
Source: http://www.techienote.com/2011/03/switching-to-gnome-in-ubuntu-11-04.html