I recently upgraded to Ubuntu 11.04 Natty Narwhal, only to immediately decide that I hated the new Unity windowing system. DON’T PANIC.
You can still use your wonderful Gnome-ness in Ubuntu with little hassle. When logging in, click on your user, and down in at the bottom there is a little selection box that says “Ubuntu”. Click on that box and select “Ubuntu Classic” and finish logging in.
There you go, Ubuntu without the terrible Unity Desktop! (Image courtesy of XPG4.net)