A while back I posted about Dual Monitor Gaming - it didn’t really work too well for the games I wanted to play, because basically you end up with the crosshair right in the worst spot possible - between the monitors. However, I broke down today and added a second GeForce 8800GTS 512 card and a third iiyama ProLite B2403WS monitor to my rig. Sweet.
Hardware installation was painless - but the monitor was disabled initially. Once I booted into Ubuntu I ran nvidia-settings and it showed the second card, and I was able to enable the monitor.