This is a rather complex gadget. When a user logs in, the gadget will read that user's email attribute (mail) and then use that attribute when subscribing a user to a list. Also, that attribute is used to display the current subscribed lists. You can also configure the gadget to:
filter out lists (so that users never see them)
email the user a results message when they subscribe/unsubscribe (you can tailor this message).
let users modify their list settings (change their settings to something like: only receive digest messages).
Email Scott if you have suggestions for enhancements.