Comment 17 for bug 290774

@chadeldridge - same symptoms as you describe happened to me after I upgraded to 9.04 - after spending an hour playing with down grading the nvidia driver and alternate monitor configurations I simply went back to xinerama and adjusted the display offset in the monitor's own adjustment menu (I have a VP171b ViewSonic). The nvidia driver maps everything correctly after this... A silly solution I know and why it happened in the first place is anybody's guess but now I have my beloved 2nd portrait monitor back...

Good luck,

-S