I installed Ubuntu 11.10 in a VM on virtualbox.
Installed guest additions. Installed "proprietary 3d driver". Installed package build-essential. And a couple of others (nothing out of the ordinary-- I was trying out node.js so I did all the packages that building that requires. Also did freeglut3 and mesa-utils)
Then I decided I'm not happy with the window manager (which is not gnome, but Unity?). I have reached this conclusion after a few hours in practically every version of Ubuntu I have ever used.
sudo apt-get install xmonad.
Select xmonad when logging in. Screen's stuck.
I was able to boot to recovery root shell from grub.
What's next? All I wanted to do was try
xmonad... This has got to be the quickest I've ever irreversibly (hopefully not. this is where you come in) borked a machine.