If you use IPB and it's not open to the public, but you want the SEO value of the content...
Snip off an abstract of the thread, e.g.-
How to Improve the SEO of IP.Board Forums by Community Member
By snipping an abstract of the thread which is loaded with SEO improvement related keywords and phrases you can get Google to index the pages which contain the abstracts, without opening up the forum to everyone.
By strategically placing a few topic related abstracts on a static web page, (or as links in an online Newsletter), e.g.- "SEO for IP.Board" or "Do Search Engines Index Forum Messages", etc.. You can gain the SEO value without opening up the content... [
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You could put leaders like this on your home page or any other page and I'm sure you'd get good SEO bang for the buck, (in effect harvesting your own un-indexed content for SEO gains). Scrape your own site, it's legal!