Happy using it for my projects:
Eve.QA - easy and expressive Q&As for events.
Oprium.com - a place to share and discover exciting opportunities.
Apteka.TJ - forum on health, beauty and family well-being.
Pros:Robust and modern FOSS forum engine.
Great core team and friendly community.
Powerful full-text search, good plugins and easy to customize.
Cons:Currently cannot:
- assign moderators and staff per-category;
- let login with phone # (i.e. without email) out of the box.
I have used it extensively in Andrew Chen's talk platform: http://talk.andrewchen.co/ and also for Write The Docs forum at http://forum.writethedocs.org/. I think it meets most of the goals of a well structured, well monitored, and custom discussion forum. I like it.
Pros:Highly customizable and modular in what exactly we need.
Cons:Bit of a learning curve while setting up first time. :)