Just wanted to add a couple links supporting the usefulness of SLI at low res in rare cases like Crysis. You have to look at the 9800GX2 which is basically SLI G92 in a dual PCB single PCI-e slot fashion.
Crysis very high:
Notice the spanking the GX2 does to a single G92 like the 8800GTS 512MB. 30 fps vs 18 fps. No single GPU hits 19 fps in this one.
1280x1024 very high no aa/afhttp://www.digit-life.com/articles2/digest3d/0408/itogi-video-cr3-wxp-1280-pcie.html
Even without fsaa/af, it's still 35 fps vs 22 fps showing the playable difference of SLI even at 12x10 no fsaa.
Now going down to 1024x768 with aa, there is still a big difference. 37 fps vs 25 fps: http://www.digit-life.com/articles2/digest3d/0408/itogi-video-cr3-wxp-aaa-1024-pcie.html
And at a puny 1024x768 no fsaa, it's 38 fps vs 27 fps average. http://www.digit-life.com/articles2/digest3d/0408/itogi-video-cr3-wxp-1024-pcie.html
There's proof right there that SLI doesn't need high resolution to scale properly. It just needs GPU demanding settings at whatever the resolution.
Anyway, you will notice that the 9800GX2 leads alot of their low res gaming tests. But in most games the single GPU's still do well enough. If you don't hit a CPU limitation, SLI can scale well at low res, whether or not you need dual gpu's to be playable is a different story. But Without question Crysis very high warrants SLI at any resolution as a single GPU struggles.
This goes along with why I think 9600GT or 8800GT SLI is a good option for people to consider over a single GPU of equal pricing. More often than not 9600GT SLI will beat a single 9800GTX, and sometimes it's a crushing. And to be honest, SLI and driver support have matured alot. It would be the rare game where it would lose because of SLI issues, and most of the time those games a single midrange 9600GT or 8800GT will be plenty anyway. It could be a new game needs a patch or driver support for sli to work properly or scale properly. But TWIMTBP usually makes that a top priority for NV to save face. Not saying there aren't good reasons to consider a single GPU vs SLI (there are), but just there are also good reasons to consider certain SLI midrange solutions over a top single gpu. The introduction of the 9600GT and low 8800GT prices have made them excellent SLI options.