How do I install and switch to the Unity 2D desktop?

I read that there is now a 2D version of Unity built on Qt. How do I install it, and once it's installed, how do I switch to it?

For 11.10, 12.04, & 12.10

Users of 11.10 and above have Unity 2D installed by default already.

To use it, logout, you will be confronted by the LightDM manager.

Then, click the little cog wheel, and select Ubuntu 2D.

Then, enter your password, hit Enter and you'll be logged into Unity 2D.

For 13.04, no need to do this - they have integrated the Unity 2D and Unity 3D environments.