At various times, which I can't pin down exactly, my 12.10 with Unity fails to lock the screen after timeout, fails to log me out when I click Log Out, fails to switch users when I command it, fails to shutdown or restart.
Sometimes I can't log into either of the two profiles that are set up on the machine and have to reboot it. Sometimes the reboot doesn't fix this and I have to shut the machine down and restart it to be able to log in.
Another thing I noticed that may or may not be related is that often, when I try to click on something in the panel on the top right that has a drop-down menu, the menu won't come down until I click on a menu on the left, drop a menu down over there, then go BACK to the right hand side and then the drop-downs will work.
This has been going on in one form or another since 11.10.