I saw thomblake's comment, not this one.

It seems to me that forums provide a better experience for very long-running threads (though such discussions would often warrant top-level posts) (being able to re-root a comment thread under a new post would be a nice feature), and better indexing (ditto both parentheticals).

(FWIW, I tried to establish an unofficial forum for OB in 2008; a maximum of about five people ever used it.)