Amazon Associates will want to pay very close attention to a recent announcement. Amazon will be renaming the Amazon Associate Web Service to the "Product Advertising API" effective immediately, but that's only the beginning.
Most important in the announcement is that affiliates will be forced to migrate to "authenticated services" and will be given a time frame of May 11th to August 15th 20009 to do so. Unauthenticated requests simply won't be processed after that date. This announcement is primarily meant for developers or those that have outsourced their programming when building applications that use the Amazon Associate Web Service.
Authentication is a process for identifying and verifying who is sending a request. For example (this gets a little heady so hang on), the sender (the affiliate) obtains the necessary credentials and send a request with that credential to the recipient (Amazon's Product Advertising API). The recipient then uses the credential to verify the sender actually sent the request, which if they did, the recipient then proceses the request.
Amazon has updated its terms of service to reflect the move to authenticated services