I received this in the mail from Amazon:
We’re writing to let you know about a change to the Amazon Associates Program. 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, and their extended search networks. If you're not sure if this change affects you, please visit this page for FAQs.

As of May 1, 2009, Associates will not be paid referral fees for paid search traffic. Also, in connection with this change, as of May 1, 2009, Amazon will no longer make data feeds available to Associates for the purpose of sending users to the Amazon websites in the US or Canada via paid search.

This change applies only to the Associates programs in North America. If you are conducting paid search activities in connection with one of Amazon’s Associates Programs outside of the US and Canada, please refer to the applicable country’s Associates Program Operating Agreement for relevant terms and conditions.