B L Ochman has an interesting post which links to the Logic+Emotion site and talks about how "blogs are what connect the community clusters".  One of the things that the post includes is this diagram where the green dots are the interaction between these communities.

What interests me about this type of diagrams is how they can be used to display large volumes of information to be able to identify trends or an overview.  One thing that marketers have problems with is the volume of data that they have to absorb and understand to be able to make informed decisions.  By looking at some different scenarios where people also have to consume lots of information it is possible to come up with some different and interesting ways to do this.