This will probably be an unpopular comment, but what's the harm in posting a thread on a previously discussed topic?
Just because a subject has been discussed before, doesn't mean:
(a) all that could be said has been said,
(b) the participants in earlier threads are the ONLY people with valid input,
(c) newcomers don't desire to discuss the subject too.
Sure, if a person wants to research a subject, the search button is there. But if he/she wants to DISCUSS it -- is the subject forever closed? And admit it, isn't it annoying when an ancient thread is exhumed from the crypt?
A forum, in my mind, is not a museum of prior conversations. A forum is a place for active discussion and lively participation.
* steps off band wagon *