I think Amazon is fairly web 2.0 in terms of user interactivity - ratings, reviews, lists, etc. They try to make it into more of an experience that just buying a book - seems to work.
I'm sure there are much better examples around though.
When you setup a lens on squidoo you can link up with Amazon, Ebay, Delicious bookmarks, ebay, flickr and more. Here is a link to have a look round - Squidoo: Build a Lens: Start Here