"The social graph"

"the social graph" -- Dan Russell (Google) used this phrase in an email talking about using data from social networking technologies.

I find it both telling and fascinating. One of the difficulties I experience personally with the use of social networking tools, and which is a critical obstacle to their use in crisis management, is that they assume a "flat" graph. I need a clustered graph: I do, want and need to compartmentalize most of my interactions, e.g., I'd use Twitter much more if I could target/hear from friends vs ISCRAM board vs ISCRAM community vs Silicon Valley Red Cross vs American Red Cross etc.

(The next step needed for crisis management is the ability to filter and screen interactions based on cluster membership and role.)

Is anyone looking at clustering for identifying and managing social groups meaningfully?