Thats true. But I'd rather get one good performance card now, and upgrade like normal, than having to buy 2 cards. Just look at the 3dfx Voodoo2 cards that were in SLI. Sure they performed great, but was it worth the money spent on it now? I think SLI's is the rich boy's alternative or hard hardcore gamers who always have latest technology.
Anyway, shouldn't one GF6600 or 6800 be enough for now?