Google did a really good job of indexing forums, they where a great place to find honest reviews, share information etc. Now they are dying with users spread across various services which are not publicly indexed making it hard to find interesting information, that and forum posts look to be now down ranked in Google in favor retail sites.
A few of the communities I am interested in such as outdoors, adventure motorcycling have moved to google groups. It's frustrating as the content isn't publicly searchable so you can not discover it, it's also frustrating posts are displayed algorithmically so it may pop up in your feed, you navigate away to another page then are unable to find the post again.
Facebook has been great in it's trivial to create communities but it's terrible in the sense content is only surfaced based on some algorithmic value biased around display adds.