This is about the numbers -vs- engagement battle. This was highlighted by Seth and Scoble back in June. There is absolutely no point in having a member in your community who doesn’t participate. It’s an irrelevant figure. If you couldn’t measure inactive members, you would ignore them right?
The opposite is to have a waiting list. What’s the maximum number of conversations you can have without overwhelming members? You can grow your community in blocks until it feels right. New people can join a waiting list. Every month you kick out the members that haven’t visited or participated and invite people from the waiting list. 1 in, 1 out.
You can really have fun with this. Why not create a quick separate group just for people on the waiting list? What would happen if they could do things that would move them up the waiting list? What if you let members voted who should be on the waiting list.
Having a waiting list costs nothing and increases the value of community. Imagine a community without idlers, a community with everyone participates.