Originally Posted by sycamorex
In the meantime, what else can I do to get to the bottom of it and/or kill X without shutting down the computer?
EDIT: I managed to kill X with killall -9 X and startx remotely. Well, that's not a solution to the problem but at least I could shut it down properly before going to sleep.
You might also try to kill x with AltGr-SysRQ-r,AltGr-SysRQ-k.
Would it be an idea to update to current to check if that solves the freeze problem?