In essence, Amazon has created a web service which can be included in Mashups just the way any other web service is. At the same time, they are attempting to solve the micropayment problem. (They aren't really "solving" it, they are simply providing it at the at the provider-to-provider level, where presumably they will add up to a single large payment, as opposed to the consumer level where people are unwilling to plop down money in advance of (possibly) making small payments in the future.)
I've always had a little trouble figuring out what Amazon was up to with their hosting services. It didn't seem to play to their overall corporate direction, image, or strengths. This, however, makes good use of both those services, and their commerce capabilities. I expect we'll see Google and eBay/Paypal make similar moves.
I'm the CEO/CTO of Somewhere, Inc., a company building a unified social networking layer that gives people the means to track their friends across multiple social networks.
