I've read some impressive reports about AMD Llano, including that it can work in setup similar to Hybrid Crossfire (ie. integrated GPU with the discrete GPU). I imagine, that this will only work with newer GPUs and motherboards. So what are hardware requirements to use AMD APU and discrete GPU in crossfire setup?
From AMD Hybrid CrossFireX Options for Desktop Llano APUs Explained it appears that there are only certain configurations of APU and GPU that will work together in hybrid mode. From that article:
Basically you have the graphics card on the left and the APU it will work with on the top and that give AMDs "configuration name" in the table. It seems that there are a limited subset of APU and GPU combinations that will actually work together.
There's more information at Hardware Canucks.