Nvidia talked openly about Hybrid SLI and has really high hopes for it. You can actually combine the integrated graphics core and the discrete graphics and still gain some performance out of it.
The first Hybrid SLI solutioin is expected in Q4, possibly in November and it should be launched for the AMD platform with Intel to follow. We are sure that this will work with both K8 and the upcoming K10 generation.
We wrote about this before here, but let me remind you. Nvidia claims that if you have the 8400GS, the slowest and cheapest DX10 Geforce 8 and combine it with a board that supports Hybrid SLI you should almost double the performance of your PC.
If you have an 8600 card and Hybrid SLI you should get up to some 20 percent of performance increase and even 8800 GTX will run slightly faster in this mode.