Joe,
>No-one else can get a graphical session on that box because the
graphical
>console is taken with the stalled session, but console logins are still
>fine and other users can freely start graphic sessions on other machines
>on the network.
What happens if somebody else tries to log on just after a reboot?
That too is fine; any other user, either after a reboot or after the
frozen XFCE session has been taken out by "kill -15"
Jonathan