When I boot my system, it goes fine right up to the GDM login screen. But now, at the login screen, no users are shown - just a "not listed?" option that brings up a username/password dialog. No joy there - "authentication failure".
I am able to login at a virtual terminal, then startx into Gnome.
F17, 32-bit, fully updated as of 9:30 this morning EDT (US East Coast), problem occurs with or without nvidia proprietary drivers.