$ sudo gconftool-2 \ --direct \ --config-source xml:readwrite:/etc/gconf/gconf.xml.defaults \ --type bool \ --set /apps/gdm/simple-greeter/disable_user_list true

Maybe they want to abandon gdm? I can already tell many users are switching to KDM if not switching from Gnome to KDE completely. Worst case, they leave for another distribution all together. Great job there redhat/fedora.