The past couple days at Etech have been filled with news of Amazon's developer API success and their future plans. There are a lot of things in store for the api, including custom cobranded checkouts and integration with z-shops and their marketplace sellers. This could mean that someday you could have your own site with your own site design that also included a storefront (of your own products) that was powered by amazon. People would then buy things from the storefront, and although they would be sent to amazon for checkout, the entire process could appear as if it took place on your site, within your design.
Amazon looks poised to take on sites like eBay/paypal and bigstep as they build a public merchant platform that can be used by all. In many ways it's a Wal Mart-ization of the web, as many small web shops opt for selling through a skinned amazon storefront and checkout system instead of using an off the shelf package or paypal and their own system.