Apple and AMD discuss partnership
According to the sources from Apple Insider, AMD representatives have been seen recently on the meeting with Apple's top brass. The discussion was about the possible partnership between these two organizations as Apple looking forward in bringing AMD's CPUs to workstations and notebooks. The main reason for changing its main processor supplier is probably the try to increase the flexibility and competitive options of Cupertino's company. Another explanation is problems, that were encountered with Intel recently (they include limited availability of recently produced processors and new chipset designs that don't allow using any video chips except its integrated graphics chip).
The reason why AMD's chips were not used by Apple before is that back in 2005 the company was interested in a news Intel Core line of fast and efficient CPUs that were suitable for use in notebooks. But now multiple sources of CPUs will allow Cupertino's company to choose the best parts for its computers on the markets. Moreover, AMD owns ATI and that might cause Apple to bring its products made of AMD and ATI components with a same great performance as before but with lower prices than Intel's.
It is possible that Apple want to customize x64 AMD CPUs for Macs in the same way as A4 ARM SoCs were customized for iPad. And AMD seems to be interesting in adopting its products for Apple's needs. Another suggestion made by Apple Insider sources is that Apple may have discussions with AMD to enforce Intel to continue retaining Apple's business. Something similar was made by Apple when it supposedly had plans to use Bing instead of Google as a default search engine on the iPhone. Nothing was changed but Google seems to have understood the hint.
If AMD will have an ability to deliver 4/5 of Intel CPU performance at 3/5 of its cost it will be definitely a new way for Apple to deliver its products with the same performance and sophistication but at the lower price.