Check here: http://forums.killermovies.com/member.php?action=editoptions
And make sure that "Use 'Email Notification' by default?" is set to no.
Visit this link to automatically unsubscribe you from subscribed threads: http://forums.killermovies.com/member2.php?s=&action=removesubscription&type=allthread
Did you click on the last thread?
Once you have told it not to auto subscribe you, you still may have threads you were subscribed to previously. Clicking on the last link will make sure you are not subscribed to *anything*.
If it still doesn't work, then do you get replies for creating new threads or also replies?