@frances for a more detailed look at how we might start to explore the structure of out personal twitter netwroks, see:
http://blog.ouseful.info/2010/09/21/small-world-a-snapshot-of-how-my-twitter-friends-follow-each-other/

A cluster analysis of my twitter personal network identifies several different clusters/distonct groupings within the folk I follow – ed techies, open data/gov folk, journalists, OU folk and JISC/Museums/Library folk

tony