I just found this pearl on Microsoft's support site. It looks like Microsoft should get some of the blame for SLI not working properly on Vista, it's not all because of nVidia's drivers. All things considered I think this is a good step forward
MS messed up, but dont forget ATI was affected just as much and still had better crossfire Vista drivers than nvidia's SLI, not to forget later released DX10 cards almost a year before ATI. So how can we NOT blame Nvidia?