After much coverage and much anticipation, ATI's Crossfire is here, and the reviews are already starting to emerge. Sadly, they aren't looking all that terrific right now. If you want to jump straight to the gaming results go ahead. In the mentioned article, the Dual X850's are being beaten by solo nVidia cards at certain points. There's a lot of reason behind that, from the way the game is designed to Crossfire emerging just recently, but ATI definitely has a lot of room to improve.
The article here talks a bit about the process involved, and helps clarify what Crossfire really is, and could potentially go. Technologically Crossfire should have no trouble keeping up with SLI, and both technologies are scalable, so I'd wager that in the next few months we'll see more card releases from ATI as well as drive improvements that'll make it much more attractive. I'll keep my eye out... ATI hasn't failed to impress in the past, and nVidia has put a lot of pressure on them, especially with the awesome 7800 GTX. Come next round, I hope we see a pickup in ATI performance.