The bug tracker has a few related items.
http://moodle.org/bugs/query.php?title=&title_type=like&description=forum+rating&description_type=like&emailsearch1=email&email1=&emailtype1=like&emailfield1%5B%5D=owner&projects=&versions=&components=&op=doquery&order=severity.sort_order&sort=asc&savedqueryname=
the docs are also interesting:
http://docs.moodle.org/en/Forum_development
But the last link hasn't been updated in some time.
Forum
Keeping track?
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