I've been really enjoying Automattic's data.blog so far, and Demet Dagdelen's post on Mapping the Communities of WordPress.com was insightful. Demet looked at the blogs in the WordPress.com ecosystem to try to determine which ones are connected to each other and how many sub-communities they form in total.
Demet was able to filter down to 109,099 unique blogs that belong in 428 distinct communities, and also drew the conclusion that photography is connected to almost everything in his results. I encourage you to check out the charts and the extensive notes that he created. This is a perfect post for data geeks.