At what point do you start rejecting invitations to join a new social network? Building your social network requires some level of investment – maintaining a profile, uploading address book, processing friend requests, etc.
At a basic level, social networking is about accessing and leveraging the relationships between people. We started with social networks as applications (the website that hosts the network) and now see the emergence of applications that are enhanced by the social network including corporate applications like email, project management etc.
I think that we're each going to be members of a core set of social networks that reflect the different grouping of relationships that we have in our lives. These include:
Business – interactions with other people as a result of our jobs/careers that will typically be in other companies and are leveraged for professional development and "door opening".
Corporate – interactions with people in the same corporations that enable idea development, team interactions etc. where sensitive or confidential information can be stored/shared.
Personal – this is our set of friends, family, relationships from school and college that we want to maintain for a long time. This is the true "social" network.
Passions – these relationships revolved around other people that share the same hobbies, sports, avocations or are grouped by common ethnic backgrounds or interests.
Transient – these relationships are short lived and result from the formation of groups of people that come together for a while and then go their separate ways – for example, parent group for kids sport team, parents of kids in the same class, or perhaps committee members of a task force in a non-profit.
There are clearly dominant players in some of these categories – LinkedIn in the Business network, Facebook in the Personal (and spreading to others) and Ning in the Passions and Transient category. Given the investment level necessary to maintain these networks, I can't see myself being a member of multiple networks in many of these categories.
There are also holes – there's no clear winner in the Corporate category as an example but perhaps that's what Cisco had in mind acquitting the assets of Tribe or where Xobni might go with its Outlook plug-in?
Holes in markets are opportunities for new products or sometimes new companies – as social networking evolves there will be new opportunities to expand and leverage the network effect.