I just installed Mint 14 on my system and I've been trying to set a monitor in portrait mode.
I have two video cards: a GTX 430 and a GTX 550 TI. The 550 runs two monitors in landscape mode (twin view), and the 430 runs one monitor in portrait mode.
I can make all three montors function as a desktop if I leave the protrait monitor unrotated. However, when I add:
Option "Rotate" "left"
to the xorg.conf file, it gets ignored.
The log says that "Rotate" is not used and "RandR" is disabled.
I'm not running Xinerama (it appears that would conflict with RandR / XRand). The effect is that the portrait monitor is blank white, though the card buffer is still being written to (I know, b/c when I reboot, the backdrop briefly appears on the portrait monitor before shutting down).
I noted in the Nvidia docs for X Server, that the option to rotate the monitor should be available in the GUI, but I don't see it. I've only tried the "Rotate" option and not the "RandRRotation" to this point.
I'm out of ideas. It may be something simple - my Linux skills are pretty rusty, as it's been a few years.
I would also point out that every time I edit xorg.conf and reboot, I gain another start button / desktop button and system tray on the task bar as well as a blank task bar stacked on top. At this point, I'm up to six task bars, system trays, and quick launch icons... I've found a few posts about this, but they don't seem to apply to my linux install. It's a separate problem, I guess, but it appears to be related to the Nvidia settings.