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Quizzical had this one called dead to rights:
You should read the press release, even though AMD is doing them a favor by allowing SLI, and nVidia probably had to pay AMD for the privilege, they still manage to poke fun of AMD.
This support isn't retroactive, looks like it's only for the upcoming AM3+ chipsets (970/990 series)
Even more interesting than this news, is when it's paired with this recent benchmark study by HardOCP:
Where 6990+6970 ("Trifire") (at the slower 6990 stock speeds) matches and in many cases tops out tri-SLI 580 system (at the much faster stock speeds). I would say it's mainly due to a lack of video memory, but there is a significant gain going from 2-way to 3-way SLI, it's just not nearly as much as you would expect and that adds no additional video memory to the equation, so maybe it's just PCI bus saturation or drive inoptimization.