Edit #3: The laptop has cut out while running Windows so this is NOT an F12 issue - something's up with my hardware.
May be a total coincidence, but I upgraded my Travelmate 4060 from F11 to F12 last week and three times since, it has just switched off without warning as if all power has been cut. When this happens I have to remove the battery for a minute to get the laptop to power on again. If I run the laptop off battery it behaves fine - and by that I mean that the laptop will run for several hours as expected rather than the battery dying after a few minutes as if it's reaching the end of its life. The battery is only about 6 months old.
I can't see any pattern to the power off and it may be nothing to do with F12 but I thought I'd mention it just in case anyone else can do a 'me too' or point me towards anything possibly relevant.
Edit - from /var/log/messages...relevant?
Nov 22 16:32:08 tm4060 kernel: metacity: segfault at 616d2078 ip 038e09e1
sp bfe1d250 error 6 in libSM.so.6.0.0[38df000+7000]
Nov 22 16:32:08 tm4060 abrtd: Directory 'ccpp-1258907528-1633' creation detected
Nov 22 16:32:08 tm4060 abrtd: Lock file '/var/cache/abrt/ccpp-1258907528-1633.lo
ck' is locked by process 1671
Nov 22 16:32:08 tm4060 abrt: saved core dump of pid 1633 to /var/cache/abrt/ccpp
Nov 22 16:32:08 tm4060 abrtd: Getting local universal unique identification...
Nov 22 16:32:08 tm4060 abrtd: Crash is in database already
Edit #2: Related to: https://bugzilla.redhat.com/show_bug.cgi?id=539450