I formatted / but I used my old home folder. I am seeing some strange behaviours in Unity that I am guessing that may be because of configuration files from Gnome 2 (that I was using in 10.10). Could this be happening? If I deleted several folders in my home, like .compiz, could I make sure there were not remnants of Gnome and if yes, which folders would they be? Thanks for any help!
Unfortunately, this is one of the problematic things about using your old home folder. You'll likely have to check your hidden folders that contain application settings (folders that begin with a .) for incompatibilities. .config is a good place to start. You might also look for things like .gnome as well. On the nVidia driver question. You probably need to try using the nVidia 173 driver as it's the one with legacy support. Lastly, nVidia-173 is available in Ubuntu 12.04. This forum thread might be of some use on getting nVidia-173 in Ubuntu 12.04: http://ubuntuforums.org/showthread.php?t=1984913