The Economist has an article about social networks in the current issue. It introduces the Dunbar Number, the number of people we can comfortably network with. This turns out to be 150. Dr Marlow, Facebook's 'inhouse sociologist' found that the average Facebook user has 120 friends, although the range is large and women typically have more than men.
Thus an average man--one with 120 friends--generally responds to the postings of only seven of those friends by leaving comments on the posting individual's photos, status messages or "wall". An average woman is slightly more sociable, responding to ten. When it comes to two-way communication such as e-mails or chats, the average man interacts with only four people and the average woman with six. Among those Facebook users with 500 friends, these numbers are somewhat higher, but not hugely so. Men leave comments for 17 friends, women for 26. Men communicate with ten, women with 16.
What mainly goes up, therefore, is not the core network but the number of casual contacts that people track more passively. This corroborates Dr Marsden's ideas about core networks, since even those Facebook users with the most friends communicate only with a relatively small number of them.
Put differently, people who are members of online social networks are not so much "networking" as they are "broadcasting their lives to an outer tier of acquaintances who aren't necessarily inside the Dunbar circle," says Lee Rainie, the director of the Pew Internet & American Life Project, a polling organisation. Humans may be advertising themselves more efficiently. But they still have the same small circles of intimacy as ever. [The size of social networks | Primates on Facebook | The Economist]
I was reminded of a study of patterns of interaction on Twitter reported in First Monday a while ago ..
In conclusion, even when using a very weak definition of "friend" (i.e., anyone who a user has directed a post to at least twice) we find that Twitter users have a very small number of friends compared to the number of followers and followees they declare. This implies the existence of two different networks: a very dense one made up of followers and followees, and a sparser and simpler network of actual friends. The latter proves to be a more influential network in driving Twitter usage since users with many actual friends tend to post more updates than users with few actual friends. On the other hand, users with many followers or followees post updates more infrequently than those with few followers or followees. [Social networks that matter. Huberman et al. First Monday]
These studies are interesting. In one way they are a little misleading though: Facebook - or Twitter - is not the sum of our network lives. That said, it would be interesting to see something which compares to what extent patterns of interconnection are similar across different communication platforms: RSS, mail, FB, Twitter, face to face, ....