Here is an interesting (draft) paper about Social Network structures in the Isabelle and Coq community, based on the main mailing lists of the two systems:

J. Fleuriot, S. Obua, Ph. Scott: Social Network Processes in the Isabelle and Coq Theorem Proving Communities. arXiv:1609.07127, September 2016.

Just a few comments of mine:

• The isabelle-users mailing list is still the main forum for Isabelle users, but Stackoverflow is gaining more and more importance. Note that I helped to bring it in form in Mar-2013 (earning a badge for 30 days of continuous activity :-), but I am rarely participating there now, because I am too busy with the classic mailing lists.
• The seasonal peaks on isabelle-users in Fig. 1 are due to the release process, which happens approx. every 8-10 months. In 2012, I started to make discussion of release candidates fully public on isabelle-users; before it was confined to isabelle-dev, which is also open to everyone, but has fewer participants.
• Page 12: “This seems to indicate that there is some clear separation of expertise when it comes to the tool.” This is correct and follows a general principle of Isabelle development: there are areas of undisputed “experts” for certain parts of the system. Thus there is a clear responsibility to make that thrive in the long term. Often this assignment is a consequence of starting that area in the first place, or investing significant work in upgrading it (e.g. by a designated PhD or research project). My recurring appearance on Sledgehammer threads is mainly technological: I am responsible for underlying infrastructure for parallel ML programming and the Prover IDE; it also overlaps with overall system integration and release management due to the add-on ATP and SMT systems.
• In recent years, I have economized my appearance on isabelle-users as follows:
  1. Incoming messages are marked as important, when the topic overlaps with my areas of expertise. I rarely answer on the spot.
  2. After some days, weeks, or months, I revisit marked message and make sure that questions are actually answered, or add a few remarks to discussion threads.
  3. During the release candidate phases, I revisit all marked messages back to the previous release (or even one before that), to make sure that old technical problems are solved or remain in a reasonably well-defined state.

  This means the mailing list also serves as an “issue tracker”. I’ve made some experiments with an explicit tracker just for the release process, but there was very little participation. Trackers tend to become a long-term storage for well-known and unresolved problems.