Richard Soderberg picks up on something Joi Ito posted that posited the idea of Amazon blogs, writing:

Amazon blogs would be a wonderful thing to watch, in the form of “25 most recent posts”; each post is a book review, with in-built Amazon linkage for easy wishlist access. As a side benefit, I’d be exposed to far more media content than I am today, with a lot more chance of being interested enough to purchase it – after all, it’s the opinions that make the most difference.

It’s true that TypePad’s quicklists with built-in Amazon affiliation linking (not to mention the model of Gizmodo) both show how Amazon blogs could work as a ready format for collaborative filtering.
In other words, people are already Amazon blogging so Amazon might as well get into the game.