Private or Public

Your new network can be set to private or public. If it is public, anyone is free to join. In fact existing Ning users can re-use their Ning Id to login to your network. I like this username consolidation, but better might be to allow for use of OpenID for your online identity.

If you would like more control over your network then set it to Private. New memberships are by invitation only. You can choose whether to allow existing members to invite new people, or leave that completely to your own control. You can also optionally allow prospective members to request an invite via a form that you can enable on your homepage