--- comment-template.php	2008-08-21 22:28:01.000000000 +0200
+++ comment-template.php	2008-08-29 15:14:22.000000000 +0200
@@ -21,10 +21,16 @@
  */
 function get_comment_author() {
 	global $comment;
-	if ( empty($comment->comment_author) )
-		$author = __('Anonymous');
-	else
+	if ( empty($comment->comment_author) ) {
+        	if (!empty($comment->user_id)){ 
+			$user=get_userdata($comment->user_id);       
+			$author=$user->user_login;
+		} else {
+			$author = __('Anonymous');
+		}
+	} else {
 		$author = $comment->comment_author;
+	}
 	return apply_filters('get_comment_author', $author);
 }