Index: src/wp-comments-post.php
===================================================================
--- src/wp-comments-post.php	(revision 25544)
+++ src/wp-comments-post.php	(working copy)
@@ -88,11 +88,13 @@
 $comment_author_url   = ( isset($_POST['url']) )     ? trim($_POST['url']) : null;
 $comment_content      = ( isset($_POST['comment']) ) ? trim($_POST['comment']) : null;
 
+$user = wp_get_current_user();
+
 // If the user is logged in
-$user = wp_get_current_user();
-if ( $user->exists() ) {
+if ( is_user_logged_in() ) {
 	if ( empty( $user->display_name ) )
-		$user->display_name=$user->user_login;
+		$user->display_name = $user->user_login;
+
 	$comment_author       = wp_slash( $user->display_name );
 	$comment_author_email = wp_slash( $user->user_email );
 	$comment_author_url   = wp_slash( $user->user_url );
@@ -111,7 +113,7 @@
 
 $comment_type = '';
 
-if ( get_option('require_name_email') && !$user->exists() ) {
+if ( get_option('require_name_email') && ! is_user_logged_in() ) {
 	if ( 6 > strlen($comment_author_email) || '' == $comment_author )
 		wp_die( __('<strong>ERROR</strong>: please fill the required fields (name, email).') );
 	elseif ( !is_email($comment_author_email))
Index: src/wp-includes/comment-template.php
===================================================================
--- src/wp-includes/comment-template.php	(revision 25544)
+++ src/wp-includes/comment-template.php	(working copy)
@@ -137,7 +137,7 @@
 
 /**
  * Retrieve the HTML link to the URL of the author of the current comment.
- * 
+ *
  * Both get_comment_author_url() and get_comment_author() rely on get_comment(),
  * which falls back to the global comment variable if the $comment_ID argument is empty.
  *
@@ -1044,7 +1044,6 @@
  * @return string|bool|null Link to show comment form, if successful. False, if comments are closed.
  */
 function get_comment_reply_link($args = array(), $comment = null, $post = null) {
-	global $user_ID;
 
 	$defaults = array(
 		'add_below'  => 'comment',
@@ -1073,7 +1072,7 @@
 
 	$link = '';
 
-	if ( get_option('comment_registration') && !$user_ID )
+	if ( get_option('comment_registration') && ! is_user_logged_in() )
 		$link = '<a rel="nofollow" class="comment-reply-login" href="' . esc_url( wp_login_url( get_permalink() ) ) . '">' . $login_text . '</a>';
 	else
 		$link = "<a class='comment-reply-link' href='" . esc_url( add_query_arg( 'replytocom', $comment->comment_ID ) ) . "#" . $respond_id . "' onclick='return addComment.moveForm(\"$add_below-$comment->comment_ID\", \"$comment->comment_ID\", \"$respond_id\", \"$post->ID\")'>$reply_text</a>";
@@ -1127,11 +1126,15 @@
  * @return string|bool|null Link to show comment form, if successful. False, if comments are closed.
  */
 function get_post_reply_link($args = array(), $post = null) {
-	global $user_ID;
+	$defaults = array(
+		'add_below'  => 'post',
+		'respond_id' => 'respond',
+		'reply_text' => __('Leave a Comment'),
+		'login_text' => __('Log in to leave a Comment'),
+		'before'     => '',
+		'after'      => '',
+	);
 
-	$defaults = array('add_below' => 'post', 'respond_id' => 'respond', 'reply_text' => __('Leave a Comment'),
-		'login_text' => __('Log in to leave a Comment'), 'before' => '', 'after' => '');
-
 	$args = wp_parse_args($args, $defaults);
 	extract($args, EXTR_SKIP);
 	$post = get_post($post);
@@ -1139,7 +1142,7 @@
 	if ( !comments_open($post->ID) )
 		return false;
 
-	if ( get_option('comment_registration') && !$user_ID ) {
+	if ( get_option('comment_registration') && ! is_user_logged_in() ) {
 		$link = '<a rel="nofollow" href="' . wp_login_url( get_permalink() ) . '">' . $login_text . '</a>';
 	} else {
 		$link = "<a rel='nofollow' class='comment-reply-link' href='" . get_permalink($post->ID) . "#$respond_id' onclick='return addComment.moveForm(\"$add_below-$post->ID\", \"0\", \"$respond_id\", \"$post->ID\")'>$reply_text</a>";
@@ -1149,7 +1152,7 @@
 
 /**
  * Displays the HTML content for reply to post link.
- * 
+ *
  * @since 2.7.0
  *
  * @param array $args Optional. Override default options, @see get_post_reply_link().