I am also having trouble running X when i upgraded to X 6.8.1
not really having troubles starting, I Have troubles with gl acceleration (mainly the fglrx ati driver) everytime i use sth that uses fglrx, the system freezes, or x11 kicks me back out to the login screen...
here is what i get in syslog...
Nov 22 23:38:59 DarkAngel kdm: X server for display :0 terminated unexpectedly
Nov 22 23:39:00 DarkAngel kernel: mtrr: 0xd8000000,0x8000000 overlaps existing 0xd8000000,0x100000
Nov 22 23:39:00 DarkAngel kernel: [fglrx:firegl_addmap] *ERROR* mtrr allocation failed (-22)
Nov 22 23:39:00 DarkAngel kernel: mtrr: 0xd8000000,0x400000 overlaps existing 0xd8000000,0x100000