Hmmm, very interesting thread. The crux of it seems that whilst SLI works for several people's setups with WoW, it does not work in others and given the fact that it is not officially supported, Nvidia will not help you out if you are one of the unlucky ones.

I would be interested to know people's experiences of running Xfire setups with multiple WoW instances on a single screen. Currently looking at a hardware upgrade myself for boxing and wanting to run 5 instances using windowsnapper on a 2560x1600 monitor. 4870x2 or GTX280?

Cheers