Insight into the world of online networks:
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?
In an article by Zephoria, a very interesting person with a lot to say. Found via an undirected link to a neighbor in my last.fm listings.
ps. for pimping last.fm, see Fred Wilson’s comments.