For those of us involved in building healthy online communities, or indeed anyone just curious of where the social web will go, the emerging science of social networks is fascinating. Tim touched on an aspect of this his last post and as practitioners we are all learning - both from academia (see Duncan Watts Six Degrees - the Science of Connected Age) and from real lessons on the ground.

The relative value of strong and weak ties is a critical aspect of this emerging science and it has some surprises.
 

The value of strong ties is understandably in the relationship itself. Online communities need a sufficient number of strong ties to sustain engagement and the  embeddedness of the most valuable contributors - so critical to growing a community. However, strong ties on their own are not enough - particularly in recruitment or periodic regeneration phases. Tim touched on this talking about the tendency to homophily in strongly connected groups; basically the danger of a small self-selected conversational gene pool talking about the same thing over and over...  

Gavin Heaton summarises some research going back to 1973 - the key findings being that the weakest ties are the most powerful in terms of disseminating information and in facilitating the move from first adopters to early adopters. A characteristic of innovators or first adopters is that they are often marginal or isolated with very small social networks; but have one-to-one or bridge relationships to larger groups. Early adopters, on the other hand, are keen to form such bridging relationships and to amplify their reputation in a broader social network.

The value of weak ties is not the (superficial) nature of the relationship but in their sheer number and diversity. Think about searching for a job. Your close friends are likely to go to great lengths to help you but their efforts are insignificant in terms of reach and effectiveness when compared with a broad set of weak ties - particularly when the internet has just lowered the threshold on taking action (how hard is it to forward a CV...). As Michael Wu points out, having a large number of weak ties enables us to crowdsource our weak ties for help.

My takeout: understand the value of both strong and weak ties in building and sustaining your online community