One thing is sure, Nvidia's dual-chip Geforce GTX 595 packs two GF110 cores. This is the chip behind Geforce GTX 580 and it is not exactly the coolest chip around. We can also deny any plans for a GF104-based dual-card from Nvidia.
The card has a dual-slot cooler with three fans on it, at least the one from EVGA does and we can expect that the card will end up quite fast.
Judging by the two 2x4 PCIe connectors the total power available to the card is 225W and we can only hope that consumption won't be too bad. It will most certainly be hot, but end users like silent fans and they kind of make peace with the fact that they are getting one very hot but extremely fast card.
AMD's dual-GPU Antilles card is scheduled to appear in late Q1 and it will also end up pretty hot and fast.