Not Locking Screen after X minutes
I was having the same issue on 12.10. Everything worked fine in 12.04, but the problem started when I upgraded to 12.10 yesterday.
I figured out that I was just misunderstanding the wording of the 12.10 Brightness and Lock settings. There are two parts. "Turn screen off when inactive for:" x minutes, which determines when the screen turns off. Then "Lock screen after:" x minutes determines how long after the screen goes off to activate the screen lock. So you have to add the two times to get the total time after which the screen will lock. Hope this helps.
I found the solution here: https://bugs.launchpad.net/ubuntu/+source/gnome-screensaver/+bug/1063682
in my upgrade to 12.10 (using the USB stick method) I found the screen never locks regardless of the settings in the system B&L setup HOWEVER if I use Ctrl-Shift-L it will lock and then will lock on subsequent screen blanks.
so there must be some legacy config option that is not affected by the Brightness and Lock utility that neglects to install the screen-saver to automatically start the daemon upon session login. Does anyone know where this might be set or if there is some other programmatic way to initiate the daemon other than having to remember to do at least one ctrl-alt-L on each new session?