HardOCP has a little write up on the announced NVIDIA SLI technology.  Rather than spit out just another rendition of this article on PCP, I decided a link to this quality work would suffice.  The major points are all hit on there and you can see the slides from the presentation that we were shown. 
That said, SLI is coming. We are going to see 6800Ultras in the market for sale this year and we can bet on dual X16 PCI-Express boards to surface as well. The motherboard makers we have talked to about the new NVIDIA SLI are excited that this technology is roadmapped even though the motherboard makers seem to know very little about it currently.