Come to think of it, I'm also getting hangs, usually after starting SM, which takes a while to start here, too many tabs open. I was blaming SM.
Today, it happened twice, first time I hit the big red button. 2nd time I walked away, came back after 5 or more minutes and the system had come back to life. It is weird because even the mouse cursor stops moving, no keyboard or anything but it does usually eventually return to life. I've been running the 12.08 versions for a while and hadn't associated the lock ups with it.
OTOH, I no longer lose a mouse plugged into the XHCI port when copying files to a USB3 drive.
Anyways, might be an idea to wait for quite a while to see if the system comes back to life