I have two portrait mode monitors (the same model but one plugged in digitally, one analog). Both worked fine (as one big visual space) when I was on Maverick Meerkat.
When I installed 11.10 I only see one monitor working and it happens to be the digital one.
gksu nvidia-settings I do not see any way to enable the other monitor.
In settings/displays only one monitor is shown and it is called "unknown", the "detect" button does nothing when clicked, the mirror setting is greyed out, and the orientation is "normal" and clicking it does not offer any other choices such as "portrait".
The motherboard is a Gigabyte GA MA 770 UD3.