I upgraded 12.3 (64-bit) to gnome 3.8 and that went fine. However, I noticed that the nouveau driver wasn’t recovering from the laptop going to sleep so I decided to try the latest NVIDIA driver (using the one click method) which also appeared to work fine. When I rebooted and logged in however, I never reach a desktop. Instead I get an alternating white and gray screen (with an active cursor). I rebooted, logged in as root and reached the desktop fine so the issue would appear to be specific to my profile.