and Expreview seem to think that three-way SLI is imminent and VR-Zone are even claiming it will launch on November 12th.
The drivers are apparently already with Nvidia's partners for testing and so are the new three-way SLI bridge connectors.
There will be limitations as to who can run three-way SLI, at least for now, as apparently the new bridge connector is quite different from the ones used for normal two card SLI.
If you remember that the 8800-series has two SLI connectors, but Nvidia never said what the second connector was for, well, it's for three-way SLI. The trick here is that the first card connects to the second and third card and the second and third card are also connected to each other.
PCI Express 2.0 might allow for three-way SLI for the lower end 8600, 8500 and 8400-series of cards, that is if Nvidia will even consider these products worthy of such a setup.
VR-Zone has a little diagram of how it all works here
while you can find some pictures that shows you the difference of the two card connectors over at Expreview here