I've never had and SLi setup and I have no idea what that would be like. I have the power for it, but never set one up like that. It would be nice to do I think.
Because since I don't have a SLI board with two cards I can give the other one to someone for Christmas too and everyone deserves a nice video cards in their system for the holidays.
Two video cards is better than one because two of anything is better than one.
I actually need it, sc2 is eating my 9800gtx for breakfast lunch and dinner. (1fps on low graphics on big maps )