In the Mark Jaquith's Subscribe to Comments users can subscribe to a post without commenting it (like in your plugin) and when so happens this record is added to wp_postmeta
post_id: the post id
meta_value: the subscriber's email
I have hundreds of these subscribtions, and they are not imported when I activate your great plugin.
How can import them with a mysql command and avoid duplications (if a post was already subscribed in wp_comments and so already imported)?