For future release, these would be nice improvements:

- Modify configlet to enable modification of invitiations e-mail "Sender" in
  Plone. 
  (This is currently only possible in config.py.)

- Automaticaly add a number of invites for new members.

- Modify configlet to enable modification of number of invites to give new
  users.

- Include expiration functionality (invitation expires after configurable
  time period).

- Do not lose invitations when re-installing.

- Use GenericSetup for installing.

- Plone 2.5 compatibility? (Perhaps a dummy @@authenticator?)
