As of version 0.100 (which will land in F15 as a post-alpha update), the polkit-gnome package will no longer install an autostart file for polkit-gnome-authentication-agent-1. Instead, each desktop environment is reponsible for making sure that an authentication agent is running.
For GNOME, this is done by gnome-session installing an autostart file with OnlyShowIn=GNOME;. Other desktop environments that rely on polkit-gnome need to do something similar.
devel-announce@lists.fedoraproject.org