This question documents how we used to inflict the mandatory login banners required on our Linux machines at work. Unfortunately, this procedure is no longer effective with Gnome 3 in Fedora 15 & 16. Gnome 3 seems to ignore the banner_message fields in gconf-editor.
Does Gnome 3 provide an equivalent procedure that allows us to present a warning message to users prior to login?
NOTE: Moving this line of inquiry to here: http://unix.stackexchange.com/questions/38420/how-do-you-implement-a-login-warning-banner-in-gnome-3