Amazon continues to set standards in e-commerce. Now they have introduced a wiki for the product descriptions. So users cannot only rate and comment the products, they can also add detail to the product features. More info and some screenshots can be found here and here.
As not all user can see this (I can’t either), this still seems to be in beta.

However, what I could see, was the link for tagging. Not sure for how long had this, as I usually buy on – and the German version usually gets the new features a lot later (the newest feature being: search inside the book! For how long did have this already?)
With the tags, you can organise the amazon content your way, and:

Because people’s tags are (by default) visible to others, a great side effect of tagging is that you can navigate among items through other people’s tags. What items have people tagged „gift“ or „Tuscany“ or „robot?“

Nice concept of commercially using two feaures associated with the so called web 2.0!