Matt Rhodes makes an important distinction:

“For some the internet offers people the opportunity for people to represent themselves in a way that suits them. They can make themselves sound much more exciting than they really are in social networks if they so choose, talking about a band they just love and not showing certain photos that might be embarrassing from the weekend.

In online communities, it is less easy to hide behind an identity. Social networks are about ‘me’ and as such it is relatively easy to create the identity that you want to portray, showing photos, having conversations and listing things in your profile that support this. Online communities are very different, they are about ‘us’ – a shared experience, aim, theme or topic. It is not your profile that counts, but your ideas, thoughts and contributions. These are less easy to hide behind an identity that may not be completely true.

This is why the overriding principle for behaviour in online communities is to be open, honest and truthful. In doing so, we often find that people find their own voice and online identity. As an online community develops and matures, we see the members grow and develop with it, finding the way they like to act and represent themselves online.”

From a different perspective, reacting to a misleading article in The Economist, Danah Boyd also insists on the difference:

“Dunbar argued for a parallel between humans gossiping and monkeys grooming. He found that there appeared to be a cap of how many people one could maintain in one’s network. This “Dunbar number” never referred to how many people you could possibly know, but how many people you could actively “groom.” Your contacts on Facebook are not equivalent to the people you groom. These can contain close and dear friends, but it can also be used as a rolodex for ties you don’t actively maintain.

The bigger issue is that performed network ties (“Friends”) are NOT the same as the personal networks that sociologists and anthropologists have historically measured and theorized about. Comparing them is futile at best and dangerous at worst. The Economist article mixes apples and oranges, creating a sense that the networks people maintain are the same that they perform through the public articulation of contacts.”