Wil Shipley of Delicious Monster and a titan in the world of Cocoa programming recently tweeted some bad news. The free Delicious Library 2 companion iPhone App has been pulled from the App Store and won't be returning. Why, you ask?
Amazon's Afilliate Program API License Agreement, section 4(e) specifically prohibits the use of the API from programs that run on mobile devices.
I doubt Wil's the only one who has used the APIs from an iPhone App, so just thought I'd spread the word. If you're doing it, you're breaking the agreement and could be opening yourself up to liability.
That aside, I think it's pretty stupid and shortsighted of Amazon to make this particular and arbitrary restriction. It's also rather vague. What about using the API from web-apps accessed from an iPhone? What about accessing it from a Mac that's tethered through an iPhone? Amazon only stands to gain from traffic being directed their way. Sure, they could try and monopolize the mobile space, but most products that use the API don't directly compete with Amazon in any meaningful way.