Include Private Messaging
As I tally the communities I still belong to, I realize that a very large chunk of them are things I would have moved on from ages ago except that I have a personal connection with other members. This connection isn't with all the members, in fact quite often it's only a handful of people that connect me to the group. It might sound like a paradox, but a necessary precondition is that I need to be able to communicate with these members outside of the normal group conversation mode. How it actually goes in practice is that these people are part of the group, so I feel obligated to maintain connection with the group so I'm exposed to that part of them, even if it's merely tangential. As a consequence, one of the things which promotes long term user retention is making sure the tools are in place for people to develop those 1:1 connections with each other. Ideally, those aren't the only thing keeping people around but rather roots underlying a healthy vibrant plant. During the dry season though, those ties are what save you. I've known sites that went through utter dark ages but held on because the last users liked each other too much to leave even when it got tough.
