Some of these responses are very uneducated, OP read cautiously.
My personal opinion on the topic is, Apple and Intel have a very close partnership. Adding AMD's processors to the basket would only spoil things and result in hurting Apple's high quality reputation. The general public think of AMD processors as low grade, or "affordable". There is some truth to that, but only to an extent. For people who do encoding and use anything that utilizes multiple threads, you'd be surprised to know that AMD's hex core processors actually keep up with i7's (quads) in most multi-processing applications, and sometimes even beat them. Considering the cost of AMD's 1090T 3.2GHz hex core processor ($275), it would be really nice to see a 27" iMac with a 1090T, or even a Mac Pro with a 1090T, or to make things significantly cheaper, AMD's 1055T 2.8GHz hex core which goes for $198. Think of bulk pricing, and you see how AMD CPU's could make Apple pricing quite a bit cheaper.
Everyone knows that Intel's high end desktop offerings beat out AMD's offerings by a significant amount, usually 10-12% clock per clock. AMD however, has usually led the market with their server offerings (blade use, grid use, etc.) due to more cores per cost. But, all of that is changing now that Intel's server offerings include Westemere's 32nm 6 core / 12 thread architecture.
The biggest pro (right now) that AMD has going for them with their high end offerings, is heat output and cost per performance. You pay less, get less than marginal performance in comparison to "equal" Intel offerings, and it runs cooler to boot. (Imagine MacBook Pro's with hex core AMD CPU's... fantastic!)
If you're a hardcore PC enthusiast, getting AMD over Intel would be silly. If your a normal user (Mac user), AMD CPU's actually make more sense. This is all my personal opinion, but being experienced with both Intel's and AMD's latest and greatest, its really hard to say Intel is actually BETTER when you factor in cost.
AMD's hex core is a fantastic processor for the price, Intel has no competition that even comes close, price wise. I would LOVE to see AMD CPU's end up in Apple products, but with Intel and Apple elbow deep in each others pockets, I really don't think it will happen.