It seems I'm not the only one to have had this happen. I'm writing this from by backup partition on the same machine, so all my hardware is still good. I have an ATI Radeon card. When I 'startx' 'Xorg.0.log' tells me: "No supported AMD display adapters were found". 'aticonfig' tells me "No supported adapters detected". From what I've read the problem is in the kernel or xorg or fglrx and that if I could 'roll back' those things I might have a fighting chance. If I rename my xorg.conf I do get the GUI to boot, but both of my monitors show the same thing, and the resolution is terrible, like maybe 640x480.
At some point during the update there were msgs regarding fglrx being in the kernel or not in the kernel or some such. FWIW, there was also an error msg to the effect that the root partition could not be determined from fstab which seems strange:
#<file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc defaults 0 0
/dev/sda1 swap swap sw 0 0
/dev/sdb2 / ext4 rw,errors=remount-ro 0 0
Any advice? As I said, my backup is fine, so I can copy over any files if that might help.