I think that I would prefer to use Unity 2d. Is there a way during a clean install to choose 2d instead of the 3d even though my hardware would support 3d? My main applications that I use are for graphic design and photography and need all the resources I can when working with large files and/or large number of photos. From all the reading, 2d is lot less resource intensive, is this true? I switched from the LTS to xubuntu, but I really would like to learn this new UI.
Sure, you can select Unity2d during the installation when installing from the minimal iso. Obviously, you'll also have to select and install the other packages manually as well.
In Oneiric Unity 2D is the fall back mode. If the hardware is not capable of running Unity 3D then Unity 2D is installed. You may find that the video drivers that come with the installation are capable of running your video card in 3D. In this case Unity 3D will be installed. I think this happened when I installed 11.10 alpha four months ago.
In this case you need to open the Ubuntu Software Center and search for Unity 2D and install the four parts of Unity 2D. Then reboot and at the login screen after you have clicked on your user name you will see a menu with the option to load into Unity 2D. Ubuntu in that menu is Unity 3D.
The login manager will usually load the last chosen mode. So, next time you boot you will already be set up to run the Unity 2D desktop.
On my system I have set myself up as two different users so I can switch between 3D and 2D without rebooting. I wanted to compare the two setups. You might find that useful.
Correction: In the menu Ubuntu is Unity 3D and Ubuntu 2D is Unity 2D. I have just tested the accuracy of my reply.