Social relations - strong and weak ties

A bit of jargon (Preece p.173):
social relations
communities & groups
strong and weak ties
social capital

The Internet supports existing strong ties, but developing strong ties with friends met online is rarer. Converting weak ties into strong ties may require face-to-face social interaction.
Putnam explains that the purpose of 'interest' groups appear to be for people to talk about themselves in the presence of the group and not to participate in a community. (Preece p23)

There are many reports of people receiving support and empathy from online relationships (Hiltz 1985, Preece & Ghozati 1998, Sproull & Faraj 1997, Sproull & Kiesler 1991). For people who are unable to attend local functions, meeting in online communities and developing weak ties is better than not meeting at all.

For well-working online communities you need good usability and socialbility:
Socialbility is concerned with planning and developing social policies that are understood and accepted by the community (registration policies).