Paul Addams discusses social networks and how online social networking websites break users' expectations for sharing and privacy. His main insight is that social networks consist of several distinct groups that do not mix with each other and that users have different ways that they share with these separate groups. This insight probably led to the creation of "circles" in Google + which allows users to bucket connections into different groups. While Facebook also lets users bucket friends into different groups, few people understand how to properly use this feature and it is not as well integrated as Google +'s offering.
Addams also goes into how purchasing decisions are affected our connections and finds that overall, the closeness of the relationship is the best predictor for influence.
Addams formerly worked at Google as their Senior UX Researcher and was part of the team that created Google +. He is currently at Facebook as a researcher.