If someone have some time, you can do the folowing modifications :

1) The possibility to subscribe to categories (multiple newsletters)
2) Something to select the mail format (text or html) when you subscribe
3) Create a better block
4) Modify index.php to display only one picture acording to your subscription options. For example, if you are subscribed, don't show the subscribe button.

This module was originally designed to be able to know how many people received the email and how many did not received the email. With the use of the Xoops class to send emails, it's not any more possible to know this information (or am I wrong ?)

PS : Don't ask me, you can't join files to the mail.

Bye,
Hervé