Abstract visualizations of del.icio.us networks

The illustration below is actually a chart of links shared between eight different del.icio.us users. I confess that I do not fully understand the methodology behind the chart, not being a del.icio.us user myself, but still, I think the concept is fascinating, and the results beautiful and geeky. You can see many more such charts, and read an essay explaining how they were developed, at Mandalbrot.net.