The source is in Amazon's Affiliate FAQ
QUOTE
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.
The gist is you can no longer bid on phrases in PPC and either send the traffic directly to the three mentioned Amazon properties, or send the traffic to your own web site and immediately redirect to the mentioned Amazon properties. If you do they're not going to pay you a commission referral starting on May 1, and if you're using their feeds they're going to cut off your access to those.
You apparently can still bid on PPC terms, send the traffic to your site then link to the appropriate Amazon page by the way I read it.









