One somewhat annoying change in Gnome 3 is the fact that Power Off is not exposed to the end-user unless suspend and hibernate are not available. If suspend does not work for some reason (buggy hardware), there is no easy way to disable it.
Recently suggestions to edit /usr/share/polkit-1/actions/org.freedesktop.upower.policy have started circulating the blogosphere.
Unfortunately editing anything under /usr/share is a bad idea: the changes will be silently overwritten by the next package update (upower for this particular file).
Thus we need something more permanent.