In the new desktop version of Ubuntu, Canonical has introduced the Unity shell which was said to replace GNOME. In the last weeks, several users have expressed on the Internet their disagreement towards this change and the impossibility to continue using GNOME.
However, that is not exactly true, since Ubuntu Natty Narwhal lets the user free to choose between these two shells.
In fact, if you prefer the older interface just
select the entry "Ubuntu classic" before logging into your own account. On the contrary, you can restore the default setting by selecting "Ubuntu".