There are enough topics on WW about Google's supplemental results, but I haven't seen one specific to online communities.
I raise this topic because one of my content sites hardly ever has any of its regular pages in the supplemental results, but the forum (about 3 years old now) has recently started getting more and more topics relegated to the supplemental.
Now, I'm aware of the many issues around forum software and duplicate URL issues and I've pretty much dealt with most of these. Or at least I opted to not fix what wasn't broken at the time - [webmasterworld.com...]
I also wonder if Google gets to a threshold on certain subject areas. For example, if a web site has 250 topics about the same subject (something easily done on an industry specific forum site), then the article/thread had better be a seriously good - and much linked to - topic or it is going into the supplemental. If a Blue Widget site has yet another posting about "Where are the cheapest Blue Widgets", I wouldn't blame Google for burying this. It's not duplicate content by any means - more like yawn here we go again content. ;)
But, I've also noticed that even unique forum topics are increasingly being stuck in the supplemental index and I'm wondering if anyone has noticed and consistency as to why this happens, or whether there are any tactics that people are using to help prevent this?
For example, have you tried using the 'Similar Links' feature in some forum software? I've tried creating static links from elsewhere on the site (similar to the front page of WW), but I'm not sure that this has had much effect.
Any success stories, failures?