@Junko - The only logical conclusion to that question is that AMD feels that ARM provides something that x86 cannot. AMD is a member of the exclusive club of 2 that can make x86 processors so for it to give up all the advantage of the established ecosystem around x86 to move to ARM is a testament that they feel they can compete better with ARM CPUs.
They did try low power CPUs with bobcat but probably found the ARM CPUs to be much better at the low power level. At the high end where it is performance at any cost they will still bring out x86 cpus.
Not sure how AMD will differentiate with other ARM providers. Rick, you did not mention X-Gene from Applied. It seems they have similar features in term of core count and interfaces and have silicon today.
There are also the existing PPC and MIPS players in this crowded market, do you think ARM or x86 will gain market share there?
AMD gave few details on Hierfalcon. On the face of it, it's hard to see how it will differentiate itself over the Intel Rangley chip shipping today, a 2-8 core 64-bit Atom with cryto and other accelerators for comms systems--let alone what I woulod expect to see in this timeframe from TI, Freescale and others.
In short, I've yet top be convinced ARM is any kind of savior for AMD.