I learned something today.
Don't use the graphical nvidia-settings program to configure your screens in linux. Just use nvidia-xconfig.
nvidia-settings is buggy and doesn't even support features like Option BaseMosaic (which is awesome, btw). And the damn screen positioning keeps shifting around and it's hard to drag them without screwing it all up.
Here's how I got my quad-display working, with rotated-vertical monitors on my [Quadro NVS 420]:
sudo nvidia-xconfig --force-generate --rotate=left --base-mosaic \
--metamodes="GPU-0.DFP-0: 1920x1200+0+3600,GPU-0.DFP-1: 1920x1200+0+2400,
GPU-1.DFP-0: 1920x1200+0+1200,GPU-1.DFP-1: 1920x1200+0+0"
That's it. No xrandr commands or anything for the rotation/positioning.