SemiAccurate claims that Apple had late stage AMD Llano based MacBook Air prototypes last spring and had been "on the verge of production".



From MacRumors:

If you are wondering why the Air wasn?t really revamped much this last time, it is because you are looking at plan B. Plan A was basically a low power Llano in an Air shell, and that would have been a really tasty machine.This AMD based design would reportedly have had much more graphics (GPU) power, and lose only a little CPU power as compared to what was ultimately released. The "Llano" is part of the AMD Fusion platform which offers a combined CPU/GPU hybrid system:Forget about the CPU (Central Processing Unit). Chipmaker AMD would like you to think instead about what it calls the APU, its Accelerated Processing Unit. The combo product uses a single die to contain, according to AMD, "a multicore CPU, a powerful DirectX 11-capable discrete-level graphics and parallel processing engine, a dedicated high-definition video acceleration block, and a high-speed bus that speeds data across the differing types of processor cores within the design."Graphics (GPU) performance has been a stumbling block for Apple in pushing its laptop designs further.

  Apple Had Late Stage Prototypes of an AMD Fusion Based MacBook Air