Multi-GPU solutions for enthusiasts is still a small market, particularly since the number of titles able to take advantage of it has a hard time offsetting the large cost involved. ATI/AMD's Crossfire is an even smaller part of that market, with Nvidia taking the lions share of those systems. However, that hasn't stopped AMD from going full steam ahead with Crossfire, and is preparing the RD790 chipset to have triple and quad Crossfire functionality.

This is a technical refresh of the 580X chipset, which brings a host of new changes. One of those changes includes a total of 41 PCIe 2.0 lanes, which can be given to up to 4 PCI x16 slots. Those x16 slots can be used to support 1, 2, 4 or even 3 cards, something that gives them a slight advantage over Nvidia offerings:

Unlike NVIDIA’s SLI, which supports dual or quad graphics cards in SLI, the improved CrossFire solution can take on three cards for improved performance. AMD claims CrossFire scaling with three cards yields a 2.6x performance increase. Two cards in CrossFire yield a 1.8x performance improvement. AMD roadmaps do not divulge how well CrossFire scales with four GPUs.
RD790 isn't very far off, and is expected to be shipped before Phenom is released. This will give motherboard manufacturers some time to include it, though I imagine it will be some time before it becomes mainstream.