Greg b has been informed.
Both ATI & NV dual cards are not really up to scratch this time around for various reasons.
They rarely are. Too many design compromises need to be made in order to create them. Many of those design compromises are either unacceptable or simply short sighted. They tend to take what should be a great card and make a mediocre card at best. Sure they tend to rip up the benchmarks but the enthusiast isn't that stupid. We know what the numbers mean and can look beyond the marketing slides. When you do, you quickly discover that these dual GPU cards are generally a bad choice in most circumstances. Their high end single-GPU offerings in SLI or Crossfire tend to be far better performers.
You can wait for companies like ASUS to take a no holds barred approach to dual GPU cards but unfortunately you end up with cards like the ASUS MARS which are too late to the party to have any significant relevance in the enthusiast market. These solutions tend to be overpriced so that argument against them factors in for some. Typically that's not their main problem but the price combined with late release it certainly becomes an issue. What we've really seen is a shift in strategy by AMD and NVIDIA. Rather than milking a GPU architecture for several generations they try to concentrate on getting a new one out every two years at most with the upgrades in between being incremental at best. They tend to use some kind of dual GPU solution to pad that six month refresh cycle just so they've got a new product to pimp. This is why I tend to avoid the product refresh cycles and await entirely new architectures. However, a refreshed product can sometimes be compelling enough for me to upgrade to it. Though this is an extremely rare occurrence. The GTX 580 is one example of a refresh that was worth while and the 8800 Ultra is an example of one that was not.
That being said, not all dual GPU cards have been trash, but they've not really been on par with what I've thought they should be. The Radeon HD 5970 was probably the last dual GPU card I liked, but I was disappointed by it's stock clocks. Easily remedied, but we have no such remedy for the GTX 590. With their current cooling solution I'd dare say that GTX 580 clocks are probably impossible to achieve in most if not any circumstances. At least realistic scenarios where the computer could be used daily inside of a full case with normal ambient temperatures.