in my company forums, when you're about to submit a post, you can't until you've clicked the "what's related" button.
This brings you a list of similiar content posts that already exist (a bit like an advanced search) and it's only when you've scrolled to the bottom that you can finally click on submit.

This is only for new threads, replies dont need to do that 'what's related" thing.
Basically it forces the posters of new topics to automatically do a search and see the results before submitting.
I think it works great.

There's also ways to make a post a duplicate of another, and then viewers are automatically taken to the original discussion.

-Zub