Here’s a detailed and interesting article by Dan Brickley about using Apache Mahout and Gephi to map non-standard networks and use traditional network analysis methods to better understand them.
Nodes are books, links are strong similarity measures. Node labels are titles, or sometimes title + subtitle. Some (the black-background ones) use Gephi’s “modularity detection” analysis of the link graph. Others (white background) I imported the 1000 clusters from the earlier Mahout experiments. I tried various of the metrics in Gephi and mapped these to node size. This might fairly be called ‘playing around’ at this stage…
The cautionary Ben Fry quote at the beginning of the article about the seductive quality of network representation is especially salient.