Are nVidia's SLI Cards Worth the Investment?

aendeuryu asks: "So there's a lot of buzz right now about nVidia's SLI architecture, which allows for two video cards to be placed in tandem PCI-express sockets on the same motherboard to share processing. Based on the relatively low price of a PCIx 6600GT, and the promise of it dipping further, it would seem like a good idea to invest in one and an appropriate motherboard, so that one can upgrade later, right? So, for anybody who's actually got the setup at home, have SLI cards shown themselves to be worth the investment?" "There are two problems with the current state of SLI:

• It's hard to tell what software companies plan to take advantage of the SLI architecture when coding their games -- Doom3 and Several Benchmark software tests show a significant improvement over non-SLI setups, whereas some games like Far Cry actually show a performance hit over single video-card setups.
  
  
• At the moment, the upgrade path actually requires two identical cards, so you'd have to choose your initial purchase extra carefully to make sure your model is still around when it's time to upgrade.

What does the future hold for SLI, or, for that matter, the ATI counterpart, AMR?"