I may go SLI eventually, but I'm glad I opted for a single GTX instead of dual GTSes.
This is the part that none of the previews mentioned (probably because they are all running fresh installs)... I had to completely remove the last ForceWare driver and profiles from my PC before the 97.02 driver would even work without crashing (it works great now), and once this was done there were a whole lot less game profiles in the driver than there used to be. Even common games like WoW and the game that came with the card (Dark Messiah) didn't have profiles. No big deal with a single card, but with SLI you'll be doing trial and error to find the best SLI mode for any game that doesn't have a profile.
On that same idea, if trial and error is all that is needed, why didn't NV hire a monkey and give it an SLI rig with a stack of games to determine which mode was the fastest...? I would've done it for free if they had flown me out to Santa Clara and let me keep the rig, and so would just about any one of us... So, why are there fewer profiles...? hmmmm...
That being said, I'm sure that NV will ramp up the profiles and improve the drivers over time, but I wouldn't expect early 8-series SLI to be quite as smooth of an experience as the mature 7-series SLI was. That's just IMHO, and I could be wrong, but I would want to know the score with SLI before buying two cards.