Eh, it'll probably be another Crossifre x1900xtx vs. 7900gtx moments... ATI's crossfire system with the x1900xtx is the big boom, then suddenly the faster 7900GTX's come in with QUAD SLI.
AMD will probably kick in something and destroy Intel once more, but I believe they will always have the edge in Mobile processors.
I checked out anandtech... x1900xtx has better performance, but the 7900GTX is more efficient, runs cooler... and the SLI is better than the Crossfire system. So when you're sticking in more than one card, NVIDIA's GTX is the way to go.