I stumbled on the section titled “friends & favorites,” at Amazon today (note, I’m not a big Amazon user), and was surprised at the multiplicity of approaches to leveraging established communities.
Bootstrapping from their prior knowledge of a person based on wishlists and favorites, they are hoping to persuade people to input their social networks (or friends, as some of you may call them) into their database. They define different types of friendship based on levels of trust. I’m not sure how long this feature has been around (although I think it appeared shortly after they closed Planetall.com in 2000).
I’d be interested to know if they have something up their sleeve. As is, the tool allows people to harness existing communities as “purchase circles,” or groups of purchasers, and as a way to find new people. I’d love it if they made this a more important part of their interface. Now I must go add all of my friends, lest my social network be underpopulated!
overstated 
I hope that give us access to all this data via the API (respecting privacy and all that). Think of all the cool things we could do!
All of this social information is coming into focus. I’d like to see an open interface to all of these information sources (e.g. blogdex, amazon, livejournal, etc.) and some identity management tools. Otherwise it’s going to get mighty confusing.
What do you mean by an open inferface? I could have the same identity and group of friends/trusted people on amazon as at epinions.com or ebay? Perhaps Blogdex’s social network explorer could have an additional feature: what’s the linkage like between this blog and the blogger’s amazon friends?
I’d worry about privacy, I reckon…