The problem with this kind of sites (IMHO) is that you need to make some serious efforts promoting it, and it's hard to promote low quality sites or something that is not yours (RSS).
yep i just integreated and tested phpBB into my drupal install (shoots myself in the head ..should be up again now.
i changed to vbulletin ! phpbb...actually no, was quite easy. There is a module for integration. But i use VBulletin now since it has better SEO than phpbb. phpbb is way too much hand-tweaking to get it to have good SEO.