Amazon is doing Microsoft a big favor in helping them pick up some ground they've lost to Google, with Amazon now using MSN as the engine behind A9. Formerly using Google powered searches, Amazon uses A9 to to search various aspects of Amazon content, and more specifically things like books and blogs. Amazon obviously has their reasons for doing such, but isn't revealing how or why, nor how switching engines will impact the performance and relevance of their searches. Google can't be happy about this one.