Amazon announced starting May 1st, they will no longer pay affiliates for sales sent to them via paid search. That means any leads through search ads on Google AdWords, Yahoo Search Marketing, Microsoft adCenter and other search ad programs. The announcement read:
After careful review of how we are investing our advertising resources, we have made the decision to no longer pay referral fees to Associates who send users to www.amazon.com, www.amazon.ca, or www.endless.com through keyword bidding and other paid search on Google, Yahoo, MSN, and other search engines. As of May 1, 2009, these paid search Associates will not be paid referral fees.
Why did they make this decision? Amazon said, "decision is based on our review of how we invest our advertising resources." In other words, they did not like competing on the paid search side with SEMs who were sending the same traffic to their site.
A WebmasterWorld thread has discussion over this announcement, where affiliates try to understand why Amazon would change their policy on this matter. Most people think it is about not wanting to compete on keyword bids with all their affiliates. Some feel it is a good way to rid themselves of affiliates, to reduce the management fees of regulating these affiliates. Others feel it is a branding issue, where Amazon could not fully control how ads looked like that were pointing to their site.
We will only display one ad per search query for advertisers sharing the same top-level domain in the display URL. This means that if you're an affiliate advertiser, your ad may not show for a query because another affiliate or the website that runs the affiliate program also has ads using the same (or a similar) domain in the display URL.
Maybe, this is another way for Amazon to mess with Google, if you remember history. :)
Forum discussion at WebmasterWorld.