AMD being NVIDIA’s rival has never really support their multi-GPU system. Rumours and a screenshot from what looks like AMD’s slide states that upcoming AMD 900 series of chipsets will in fact support SLI. There will be two chipsets that support the feature. The first will be 990FX which will support 3-way SLI as well as 2-way SLI. The other chipset, 990X will support only 2-way SLI.
Enthusiast gamers can choose to setup SLI on the AMD platform
The new chipsets will be designed for the Bulldozer processor launch. The 9-series boards should be launched around May this year. The launch of such chipsets would mean that AMD users would be able to setup SLI solutions using NVIDIA graphics cards. Intel too has support for SLI through some of their chipsets. NVIDIA specifically hasn't designed any boards for AMD and Intel for the last couple of years.