Subscribe to Comments is another wordpress plugin which bloggingtips.org uses and which i would recommend adding to your plugins on your site. Its a very straight forward plugin that adds a checkbox for anyone who is commenting so that they can get email notifications of the post they are commenting on. The same way that thread subscription works in bulletin forums.
It should hopefully encourage your commentators to return when more comments are posted.
The plugin allows you to set the checkbox as checked as default and you can also change the text to manage subscriptions too.
Download : Subscribe to Comments
