Default to Unity 2D

Ubuntu 11.10 comes with Unity 2D for older hardware, which you can select from the log in menu. The 2D mode is for older hardware which can't run 3D Unity, the problem is that once you change the session to 2D, it defaults to 3D upon reboot. This is annoying. So how to change this:

Open the terminal (CTRL ALT T) and enter this command: (it 'll ask for your login password which you won't see while typing)

sudo sed -i 's/user-session=ubuntu/user-session=ubuntu-2d/g' /etc/lightdm/lightdm.conf

Now, reboot your PC and it will default to 2D session. Enjoy!