Upgrade to Ubuntu 11.04 without Unity

The new Ubuntu release 11.04 Natty contains the new Unity desktop environment which is quite controversal. I have tried it for a while and I think it is neat but too buggy and immature. However, it is easy to revert to the old Gnome 2 desktop environment and have things working almost as in 10.10.

First do a normal distribution upgrade to 11.04, then go to System Settings -> Login Screen and select Ubuntu Classic as default session and reboot.