I see this benifitng the people who don't want to SLI two 7800GT/X's or two 6800GS/T. But rather those that want high end performance on a cheaper budget. Such would be using quad SLI with the 6600 cards. That would be insane! You get 4 GPUs, 32 total pixel pipelines, and insane total memory and core clocks. It's awesome. I wouldn't SLI anything higher then the 6600 series cards. Just doesn't seem like a logical thign to do because games wouldn't even be able to utilize cards 3 and 4. So it's basically a waste of money.
I do liek this idea, because it give me the idea for my next upgrade to not buy a 6800xx or a 7800GT/X but rather four 6600GTs. That would be some awesome graphics!