Danah Boyd has an excellent post entitled Attention Networks vs. Social Networks which tackles some of the issues we've faced while designing Social Networking for Windows Live. She writes

The vast majority of online social networking tools assume that users are modeling friendship and thus if you're friends with someone, they better damn well be friends with you. As such, they use undirected graphs and you are required to confirm that they are indeed your friend.

Well, what about fandom? Orkut actually put the concept of fan into their system, but in order to be someone's fan, you had to be their friend first. Baroo? I've noticed that Friendster introduced fans, although it is not consistent across the site; the system decides who is celebrity. I can be a fan of Pamela Anderson but i cannot be a fan of Michel Foucault or Henry Jenkins. While i can understand that the former is clearly a Fakester, the latter is actually a real academic with a Friendster Profile that i genuinely admire (far more than Ms. Anderson). Even on MySpace where bands have a separate section, i have to add them to my friends; i cannot simply be fans.

The world is not an undirected graph and very little about social life online is actually undirected. Many social relations are unequal; they are rooted in directional graphs - fandom, power, hierarchy. So why do we use undirected models?

Of course, there are many systems that have directed graphs. I can read blogs by bloggers who who don't read me; blogrolls are directed. I can have friends on LiveJournal that do not reciprocate. I can subscribe to del.icio.us feeds of people that i admire without forcing them to do the same. I can make a Flickr user a contact simply so that i can watch their photos. I do all this because i know the world is not undirected.

Part of the problem is that we've built a model off of social networks instead of attention networks and there's a very subtle difference between the two. Attention networks recognize power. They recognize that someone may actually have a good collection of references or be a good photographer and that someone else may want to pay attention to them even if their own collections are not worthy of reciprocation. Attention networks realize that the world is not an undirected graph.

There are many good reasons to use attention networks in systems instead of social networks. Do you really want to force people to get permission to subscribe to public material of someone else? Do you really want to put people through the awkwardness of having to approve someone that they don't know simply because one person respects the other? Of course, the awkwardness of social networks does not disappear simply by having directed graphs. Reciprocity is still an issue whenever the networks are performative (visible as a statement of connection). This is most apparent in the blogging community where people feel insulted that they are not included on the blogroll of a blog that they read regularly.

This is a pretty good summary of some of the key issues folks like Mike and myself had to work through when building our Social Networking feature set. There definitely is a key distinction between attention networks and social networks, unfortunately a lot of social software applications have conflated the two. Even worse, thanks to the proliferation of social networking tools, many users have difficulty adjusting to dealing with attention networks. An example of this is the awkwardness Danah describes when people become upset because they aren't on your blogroll and vice versa.

I definitely have a lot of thoughts in this area but I'd like to wait until we've shipped before touching on this topic in more depth.