Trek over to THG, and you will find that Gigabyte has developed a 2 GPU-on-single card design, using 2 6600GT cores and the SLI bridge. Performance? Better than a 6800 ultra and ATIs X850 PE! Bad news? You still need an SLI-capable motherboard. Good news? It will probably be cheaper than a standard 6800 Ultra!
Now all we need is SLI-capable boards with one x16 slot for less than $200. Who knows what a dual 6800GT would do?