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.
They would need to use something like bitpay, but since this is amazon we are talking about, it would probably make more sense for them to roll out such a service themselves. They might even make an exchange of sorts meant only for amazon <->bitcoin users to get around relying on MTgox's recent horror shows. This would be a very expensive investment in a currency that so far has been very unstable.
By providing the exchange, AND holding a good deal of the currency -- they could buy up 40% of the bitcoins in existence easily right now -- they could actually make the market and hold prices more stable just by selling their own reserves during runs and buying during crashes.