****** FIRST AND FOREMOST READ THIS ENTIRE POST *AND* POST #8 ******
4. When setup completes, reboot. Leave your USB drive connected. When the UniBoot loader appears on screen, Now choose your Mountain Lion disk instead of the Installer (or USB or whatever you named it). It is a good idea to use a -v boot flag, just so that incase it does hang, you can see where its occurring.
5. Most likely, your machine will hang. If it does, reboot again, and now boot with a -x boot flag. This SHOULD get you to desktop.