I've noticed that it's an available feature on Weebly, which hosts our site.
Any member could start a conversation thread about, say, where s/he saw a great bargain at a nursery, or if s/he just divided her irises and is looking for good homes for the extras, or is s/he has a question that s/he would like input on from the membership. Any and all other members could reply. For instance, I know that sometimes I receive queries from other members via email that I then pass along to another gardener who might have more expertise than I. In that instance, the forum could cut out the middle man, and help other readers who have the same question.
We could use it for anything we'd like, and we can control the privacy settings, just as we do with the membership directory. I think it can be a fun and useful way to keep in touch.