My computer has a NVIDIA Quadro 1800 FX card, and I just bought a second one, in order to run four monitors. I'm using the proprietary NVIDIA driver, and the second GPU shows up in the NVIDIA X Server Settings.
The only option it shows when I try to enable it is "Second X Screen", so now I have X screen 0 and X screen 1. However, the X screen 1 does only shows black, and an "X" cursor when I move the mouse into it. How can I configure it to extend the Unity desktop over to the second X screen?
Update: I enabled Xinerama and rebooted, and both monitors showed up when I got to the login screen. However, when I tried to login, the login prompt disappeared, and it never got to my desktop. It was just stuck with the login screen background. The only way to get back into my account was to Ctrl+Alt+F1 and delete the