Thanks for the config, looks like nvidia. To be honest, I want RandR to work properly with the open radeon driver and gdm to start.
With vmlinuz-3.3.4-5.fc17.x86_64 I have the exact same behaviour, but it worked when I first installed Fedora ~2 days ago. Must have come with an update and it doesn't appear to be the kernel driver in 3.5?
Here is another scenario:
boot with the external monitor connected
just the background image and mouse pointer, where gdm should be
disconnect it and restart Xorg (ctrl+alt+bksp)
gdm comes up and I can login
wait for Gnome to start
connect the external monitor and I get a kernel oops (tested twice)
p.s. its not a big deal, since I have a workaround, I just thought I would ask if this is a known problem...