Index: wp-includes/post-thumbnail-template.php
===================================================================
--- wp-includes/post-thumbnail-template.php	(revision 17444)
+++ wp-includes/post-thumbnail-template.php	(working copy)
@@ -48,6 +48,45 @@
 }
 
 /**
+ * Update cache for thumbnails in current loop
+ *
+ * @since 3.2
+ */
+function update_thumbnail_cache() {
+	global $wp_query;
+
+	// return if not at loop start
+	if ( 0 != $wp_query->current_post )
+		return;
+
+	$cache_key = 'thumb_cache:' . md5( implode( ',', wp_list_pluck( $wp_query->posts, 'ID' ) ) );
+	
+	// return if this loop is already cached
+	if ( wp_cache_get( $cache_key, 'thumbnails' ) )
+		return;
+
+	$thumb_ids = array();
+	foreach ( $wp_query->posts as $post ) {
+		if ( $id  = get_post_thumbnail_id( $post->ID ) )
+			$thumb_ids[] = $id;
+	}
+
+	if ( ! empty( $thumb_ids ) ) {
+		$thumb_ids = array_filter( array_unique( $thumb_ids ) );
+
+		get_posts( array(
+			'update_post_term_cache' => false,
+			'include'                => $thumb_ids,
+			'post_type'              => 'attachment',
+			'post_status'            => 'inherit',
+			'nopaging'               => true,
+		) );
+	}
+	
+	wp_cache_add( $cache_key, 1, 'thumbnails', 86400 ); // 1 day
+}
+
+/**
  * Retrieve Post Thumbnail.
  *
  * @since 2.9.0
@@ -57,11 +96,15 @@
  * @param string|array $attr Optional. Query string or array of attributes.
  */
 function get_the_post_thumbnail( $post_id = null, $size = 'post-thumbnail', $attr = '' ) {
+	if ( in_the_loop() )
+		update_thumbnail_cache();
+
 	$post_id = ( null === $post_id ) ? get_the_ID() : $post_id;
 	$post_thumbnail_id = get_post_thumbnail_id( $post_id );
 	$size = apply_filters( 'post_thumbnail_size', $size );
 	if ( $post_thumbnail_id ) {
 		do_action( 'begin_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size ); // for "Just In Time" filtering of all of wp_get_attachment_image()'s filters
+
 		$html = wp_get_attachment_image( $post_thumbnail_id, $size, false, $attr );
 		do_action( 'end_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size );
 	} else {