Who cares if it's single GPU or multi-GPU? The GX2, albeit a botch job, is a single card that can run on any motherboard with a PCI-E port, it does not require an SLI capable platform, and it functions as a single card.
Nvidia will not be able make a dual GPU card with this architecture until they shrink it. The GX2 is $175 cheaper and often performs better than the GTX 280, anyone, even someone who hates multi-GPU, can see that only somebody out of their mind would buy the 280 over the GX2.
Sure, it's a single GPU that performs as well as the last generation multi-GPU, but at it's current pricing, it's not a good buy.
I can see that it's a great achievement as far as single GPU performance goes, but that doesn't make it a great card.
But I can see we're not going to agree so let's just end our argument here.