Many moons, ago when Flickr first introduced the ability to categorise some people as "friends", David Weinberger wrote about the issues use of the word gave him and how he felt disinclined to categorise people using a word that was so difficult to define. At the time I followed his lead and only had contacts in Flickr. But then I wanted some photos to only be seen by some contacts and not others .....
It is always interesting watching Robert Scoble "manage" the number of people he connects with within social tools, which for those of you who don't know Robert numbers in tens of thousands. He just followed me from his new second Twitter identity "notsecretscoble" which he is using to subdivide the people who connect with him. He has opened it up so anyone can follow this new account but he will only follow people he has met face-to-face. I have the same sort of gradations of connections with people I know and manage the distinctions with things like Friendfeed and subgroups within Google Reader.
It relates to the Dunbar number - "a theoretical cognitive limit to the number of people with whom one can maintain stable social relationships" of 150. Tools like Twitter and contact databases allow us to extend this number by making it easier to "remember" more people and track how and where we met and what sort of relationship we have with them. I use Daylite as a contact manager for keeping track of my business relationships, which now number thousands, and when I scan through Daylite I "know" all of them. At the same time I don't "know" anything like all of the people who follow me on Twitter.
It is the classic problem of signal to noise. If I do nothing the number of people I end up knowing just causes noise in my life, if I put in a little bit of effort I can increase the signal to noise. A lot of this is about energy for me - how much certain people make me feel energised and engaged and how much energy I feel incilned to put into the relationships. This has long been the case with a relatively small group of wonderful blogger friends I know and now even within the business subset of people I know I group them by how much of a buzz working with them gives me. The basis for these judgements vary all of the time and are far from hard and fast rules but are they really that different from the judgements we all make about who to become closer to in the "real" world?