As a point of comparison with my last post, here's another Network of Twitter lists.

Instead of using my main account, this was built from a separate "follow-back" account I check on occasionally, which posts no genuine content whatsoever. All the accounts listing it are themselves follow-back bots or promotional accounts (lots of rappers and penny stock experts represented).

The "follow back" hairball.

I'm going to guess this is what happens when there are lots of accounts using some auto-listing utility. When compared to a network structure based on actual common interests instead of strategic Twitter-usage, the difference is striking.