As mentioned by bit-tech a short time ago, NVIDIA have finally released a working beta driver which enables Quad SLI goodness with a pair of GeForce 7950 GX2s. It's taken a while for them to get it right, and although this driver is still in beta stages it's good enough to offer fully functional Quad-SLI power to a capable system (providing other elements check in ok, such as power supply, motherboard, etc.)

Also worth reading, hardware enthusiast website HardOCP have been lucky enough to ask NVIDIA's SLI Product Manager "Chris Daniel" some questions regarding Quad SLI.

The first implementation of NVIDIA's Quad SLI was promising, but buggy. There was a lot of work to be done on drivers, and the hardware implementation was such that you required a huge case to house the 312mm long video cards. This - and the fact that the drivers were still in development - meant that Quad SLI was limited to system builders only.