Well, I think we should not create pseudo duplicate content this much.
It's ok to use and implement sitemaps, but there is no real point to add a new page for the content itself.
This kind of mod could to be good if phpBB was not SEOed at all, bots would just "think" the real board it the one created with the mod and would barely not visit the forum itself.
But if you SEO phpBB, you'd end up creating some competition between the content in forum and the content listed by the mod using different urls.
It's not exactly as duplicate, as url are different, but still, it can create some confusion and PR loss as two pages with the same content will at least most likely mean less links for the forum one than if it was the only one.
It's more or like like adding a printer friendly version of our content, not necessarily taken as spam indexing by SEs, but still some confusion if both are optimized.
And personally, as a regular user, I don't like this much to fell on printer friendly view of the content after a search query.
I am not sure it's the best way to take advantage of the effort we put in our design
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