Comment 25 for bug 335447

My test that gnome-settings-daemon is responsible was wrong. It's actually gnome-screensaver. I also get

16:48:45.602: computer_logicaldev_input_3 condition ButtonPressed = coffee

which is the FN-F2 here and has a lock symbol on it. Starting

 $ gnome-screensaver --no-daemon --debug

also shows

[listener_dbus_handle_system_message] gs-listener-dbus.c:1481 (16:47:34): obj_path=/org/freedesktop/Hal/devices/computer
_logicaldev_input_3 interface=org.freedesktop.Hal.Device method=Condition destination=(null)
[listener_dbus_handle_system_message] gs-listener-dbus.c:1496 (16:47:34): Coffee key was pressed - locking
[gs_manager_set_lock_active] gs-manager.c:418 (16:47:34): Setting lock active: 1

So I've no Idea why at least this doesn't work for you when running gnome. Anyway, reassigning to GNOME maintainers, because the base seems healthy.