Even today, though vendor support for SLI is less than stellar, it has taken off and remains one of the most popular ways to deck out newer systems. Of course, if you can add two cards to a system it'll only be a matter of time before people want to add three.
Thus, it's no big surprise at all to see Nvidia getting ready to make three-way SLI possible. In about a month from now, Nvidia will likely be launching their refresh to SLI with the ability to put up to three cards in such a configuration. There are a few caveats: It requires new drivers, a particular chipset and particular cards:
However, to get 3-way SLI up and running, there are a few requirements. Firstly you need a 3-way SLI drivers. Secondly, you need either a 680i SLI or the upcoming 780a/780i SLI board with at least 3 PCIe x16 slots. Thirdly, you need either GeForce 8800 Ultra or GeForce 8800 GTX cards as these cards have 2 SLI connectors on each card. Even the upcoming G92 cards will not support since it has only 1 SLI connector. Fourthly, you would need a 3-way SLI bridge card.
All of that sounds very expensive, but sometimes extreme performance comes at a cost. Still, even if it costs an arm and a leg, it's impressive to think of and even nicer to look at. Just make sure you have a 1500W PSU ready to handle the load of your new space heater.