I want to make sure you all know the recent changes to Amazon's Operating Agreement.
First, and this was announced pretty prominently, they will no longer allow direct-to-Amazon PPC advertising. You can still use PPC to promote your site.
Second, and this they did NOT announce, just quietly changed the terms and started not paying commissions, they will no longer pay the 10% commission on Kindle ebooks. The rate is now 0%. There's been some protest about this--if you want to know more, check the Kindle Ebook discussions at the Associates Discussion Boards. And if it effects you, let Amazon know about it!