Don't List Sub-Forums
Drupal's flatforum module lists all sub-forums on the main forum page by default. We have modified the behavior with our own drupal theme (which is closed-source).
- On the main forum index page, instead of listing sub-forums as if they were on the same level as their parent forum, don't list them at all.
- Show a list of sub-forums as part of the forum description for all forums.
- Aggregate the statistics (post count, topic count, latest post) over all sub-forums and the forum itself.