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.)
NVIDIA has released a beta driver enabling Quad SLI with a pair of the recently-released GeForce 7950 GX2's.
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.