I was wrong, over on ValuingNetworks when I originally said Amazon didn't have network magic.
Amazon get a huge amount of value by creating networks of interactions between their customers.
customers write reviews for each other
customers build recommendation lists for each other
Amazon connect products in a network (people who bought book X also bought book Y)
Amazon calculate further recommendation lists from buying patterns : customer's "just like you" bought this list.
The Amazon database is full of links between customers, between items etc.
See also :