Hi. I am using the default twentyten theme and have wp_enqueue_script('comment-reply') enabled in the <head> of my theme. As per the Codex, when a user replies to a comment, 'Leave a Reply to %s' should be invoked.
With wp_enqueue_script('comment-reply') enabled however, 'Leave a Reply' is returned rather than 'Leave a Reply to %s' (i.e. the linked name of the comment author does not appear). When I comment out wp_enqueue_script('comment-reply') I DO get the linked name of the comment author, but am now missing the lovely inline comment form (the comment form remains at the bottom of the page below the very last comment).
// default comment_form values abbreviated below...
'title_reply' => __( 'Leave a Reply' ), 'title_reply_to' => __( 'Leave a Reply to %s' ), 'cancel_reply_link' => __( 'Cancel reply' ), 'label_submit' => __( 'Post Comment' )