Index: wp-includes/media.php
===================================================================
--- wp-includes/media.php	(revision 14979)
+++ wp-includes/media.php	(working copy)
@@ -484,6 +484,10 @@
  *
  * The url path will be given, when the $size parameter is a string.
  *
+ * If you are passing an array for the $size, you should consider using
+ * add_image_size so that a cropped version is generated.  It's much more
+ * efficiant then having to find the closest sized image.
+ *
  * @since 2.5.0
  *
  * @param int $post_id Attachment ID for image.
@@ -587,6 +591,11 @@
 /**
  * Get an HTML img element representing an image attachment
  *
+ * While $size will accept an array, it is better to register a size with
+ * add_image_size so that a cropped version is generated.  It's much more
+ * efficiant then having to find the closest sized image.
+ *
+ *
  * @uses apply_filters() Calls 'wp_get_attachment_image_attributes' hook on attributes array
  * @uses wp_get_attachment_image_src() Gets attachment file URL and dimensions
  * @since 2.5.0