Since I upgraded from 11.04 to 11.10, my login screen reverted back to landscape mode, and only goes to portrait mode (what I want) once I login.
How to make the login screen be in portrait mode?
This worked for me on a CLEAN install of 11.10:
Side-effect: I assume you have
in your "xorg.conf" file (I don't know how you'd be able to get a portrait display after logging in otherwise).
The only side effect I've noticed is that every time you use APT or Synaptic to install anything, and follow the process in the terminal screen, you'll get lots of "RandR extension not found" messages. It hasn't had any detrimental effects on my end.