Index: wp-admin/includes/dashboard.php
===================================================================
--- wp-admin/includes/dashboard.php	(revision 17378)
+++ wp-admin/includes/dashboard.php	(working copy)
@@ -707,7 +707,7 @@
 		<div id="comment-<?php echo $comment->comment_ID; ?>" <?php comment_class( array( 'comment-item', wp_get_comment_status($comment->comment_ID) ) ); ?>>
 			<?php if ( !$comment->comment_type || 'comment' == $comment->comment_type ) : ?>
 
-			<?php echo get_avatar( $comment, 50 ); ?>
+			<?php echo get_avatar( $comment, 50, 'mystery' ); ?>
 
 			<div class="dashboard-comment-wrap">
 			<h4 class="comment-meta">
Index: wp-admin/includes/comment.php
===================================================================
--- wp-admin/includes/comment.php	(revision 17378)
+++ wp-admin/includes/comment.php	(working copy)
@@ -148,7 +148,7 @@
  */
 function floated_admin_avatar( $name ) {
 	global $comment;
-	$avatar = get_avatar( $comment, 32 );
+	$avatar = get_avatar( $comment, 32, 'mystery' );
 	return "$avatar $name";
 }
 
Index: wp-admin/options-discussion.php
===================================================================
--- wp-admin/options-discussion.php	(revision 17378)
+++ wp-admin/options-discussion.php	(working copy)
@@ -203,7 +203,7 @@
 <th scope="row"><?php _e('Default Avatar') ?></th>
 <td class="defaultavatarpicker"><fieldset><legend class="screen-reader-text"><span><?php _e('Default Avatar') ?></span></legend>
 
-<?php _e('For users without a custom avatar of their own, you can either display a generic logo or a generated one based on their e-mail address.'); ?><br />
+<?php _e('For users without a custom avatar of their own, you can either display a generic logo or a generated one based on their e-mail address. This doesn\'t apply in the Administration area, where only custom avatars will be displayed.'); ?><br />
 
 <?php
 $avatar_defaults = array(