No no no no - too big, too soon.
You're not thinking clearly. I'm very bearish about the future of bitcoin, but this would be a really good thing for bitcoin. Amazon isn't just a giant online marketplace, it also has huge cloud resources and enough IT horsepower to render needing dozens of other exchanges pretty moot.
What exactly would Amazon do with the Bitcoins? They can't pay their employees or maintain their servers with it. Amazon would be the only major store taking Bitcoins. They would become bloated and Bitcoin would be worthless. Rick is right, it is too big and too soon. Economies need to cycle money and Amazon wouldn't have anywhere to put the Bitcoins after they have been paid.
Overstock accepts bitcoin and they keep 10% of bitcoin related profits on their books