If its the nvidia SLI Im thinking of, the idea behind is it saves you power by turning off your video card when not needed and running off onbaord graphics.I thought I read 9000 series and up was supported, I could be very well wrong.And yes as mentioned before in another post, your video will be somewhat slower on certain applications, gaming is 1 of them. I believe Toms Hardware has reviews on the SLI, think this is were I read about it.
Cattb