SLI/crossfire has been out a while now, and I have yet to see a micro-ATX version... shure, shuttle and others have SLI SFFs.. but those are barebones systems. anyone seen 'em?
Evga do one: http://www.scan.co.uk/Products/ProductInfo.asp?WebProductID=372829 but thats the only one currently available.
I *think* its because the middle one in Non-sli, the outer ones are, so for just running one card using the centre.