I have taken to using Facebook as a place where I put a second copy of something I've already written and published somewhere else. That ensures that in some way I'll be able to find it, probably by googling my blog posts. Things written on Facebook disappear into the ether too quickly (including this thread which will die quietly when we are all done with it).
Facebook Communities suffer from the problem that they don't really provide an equal forum for all people to share jointly in a topic discussion. Rather, they bias towards the moderator's interests, because only the posts from the moderator are visible for long enough to get any traffic.
The problem of how to build forum software is old and solved. The MTS Confer system and others that followed it like Picospan and Caucus lived in a world where you could create a long-running discussion that focused on one topic and where you could keep that topic mostly on-topic over an extended period of time. Facebook, in contrast, feels more like a big chat room, where yesterday's posts scroll off into nothingness and where you can't get back to any discussion you once had - no matter how good it was.
Twitter doesn't give you the paragraph-sized chunks of discussion that you need to actually have an intelligent conversation, but it does have long-lived hashtags that enable a community of interest to form and (with scheduled chats) thrive. It's possible to find people who you don't know who share an interest and to communicate with them in such a way that a simple enough search brings back something useful. Nothing on Facebook behaves that way.
Further reading -