I have no idea if it is related, but twice with F16
I've had Gnome completely lock up.
The mouse pointer would move,
but otherwise the screen was completely unresponsive,
not even any of the keyboard hot
keys would work (Alt-F*, ctrl-alt-del, etc).
FWIW, I am seeing exactly same response on F14
complete lock up, pointer moves.
I was not able to ssh in from my wife's iMac (normally, I can)
this version of F14 was from a fresh install, hardisk install from the iso.
I have another version of F14 (preupgrade from F12) which I am using now,
that is not experiencing this lock up
Jack