TL;DR Get segmentation faults in gnome-shell try uninstalling extensions
I woke up on the weekend to be told by my girlfriend that the main computer wasn't working. So I turn it on a sure enough it wasn't, it would boot then start loading Fedora 16 and fail at the last minute. I dropped into a shell and ran a
yum update thinking that it was my graphics drivers that were out of date. The evening before I had run and update and didn't pay attention to what was being updated.
That didn't work but I managed to get gnome to load the login screen in fallback mode (I don't know how, it just happened after the update). I tried logging in but found the gnome-shell wasn't working. I had to force my account into fallback mode from the command line using
dbus-launch gsettings set org.gnome.desktop.session session-name 'gnome-fallback'.
Trying to start gnome-shell from the command line gave me an error "Segmentation Fault". I googled around and it looked like the culprit was likely an shell extension. So I uninstalled the three I had installed, dock, alternative status menu and user theme. I reboot and gnome-shell starts, hell yeah. I reinstalled the alternative status menu and user theme (didn't install dock as I didn't need it any more, could be the culprit) and rebooted and everything started. I had to force gnome back to gnome-shell using
dbus-launch gsettings set org.gnome.desktop.session session-name 'gnome' but I was back in business.