Asus dual-7800GT-on-single-card review
Basically, it performs like a pair of 7800GTs in "normal" SLI, so I guess it's a good design. One would hope that by being on one card that performance might be better, but I guess that's the nature of SLI. It looks like you don't even need to upgrade your power supply to run it, since it has an external power supply via AC adapter!
Interestingly, you can run it in non-SLI, as it supports quad-monitors. It might actually be a decent workstation card, provide you can fit it in your case.
Give what you cannot keep to gain what you cannot lose.