Index: /Users/denis/Sites/wp/wp-includes/comment-template.php
===================================================================
--- /Users/denis/Sites/wp/wp-includes/comment-template.php	(revision 10988)
+++ /Users/denis/Sites/wp/wp-includes/comment-template.php	(working copy)
@@ -193,7 +193,11 @@
  */
 function get_comment_author_url() {
 	global $comment;
-	return apply_filters('get_comment_author_url', $comment->comment_author_url);
+	$url = apply_filters('get_comment_author_url', $comment->comment_author_url);
+	if ( $url == 'http://' ) {
+		$url = '';
+	}
+	return $url;
 }
 
 /**
@@ -228,11 +232,15 @@
 function get_comment_author_url_link( $linktext = '', $before = '', $after = '' ) {
 	$url = get_comment_author_url();
 	$display = ($linktext != '') ? $linktext : $url;
-	$display = str_replace( 'http://www.', '', $display );
-	$display = str_replace( 'http://', '', $display );
-	if ( '/' == substr($display, -1) )
-		$display = substr($display, 0, -1);
-	$return = "$before<a href='$url' rel='external'>$display</a>$after";
+	if ( $display ) {
+		$display = str_replace( 'http://www.', '', $display );
+		$display = str_replace( 'http://', '', $display );
+		if ( '/' == substr($display, -1) )
+			$display = substr($display, 0, -1);
+		$return = "$before<a href='$url' rel='external'>$display</a>$after";
+	} else {
+		$return = '';
+	}
 	return apply_filters('get_comment_author_url_link', $return);
 }