Index: src/wp-admin/includes/schema.php
===================================================================
--- src/wp-admin/includes/schema.php	(revision 52607)
+++ src/wp-admin/includes/schema.php	(working copy)
@@ -401,8 +401,7 @@
 		'siteurl'                         => $guessurl,
 		'home'                            => $guessurl,
 		'blogname'                        => __( 'My Site' ),
-		/* translators: Site tagline. */
-		'blogdescription'                 => __( 'Just another WordPress site' ),
+		'blogdescription'                 => '',
 		'users_can_register'              => 0,
 		'admin_email'                     => 'you@example.com',
 		/* translators: Default start of the week. 0 = Sunday, 1 = Monday. */
@@ -555,8 +554,6 @@
 
 	// 3.0.0 multisite.
 	if ( is_multisite() ) {
-		/* translators: %s: Network title. */
-		$defaults['blogdescription']     = sprintf( __( 'Just another %s site' ), get_network()->site_name );
 		$defaults['permalink_structure'] = '/%year%/%monthnum%/%day%/%postname%/';
 	}
 
Index: src/wp-admin/options-general.php
===================================================================
--- src/wp-admin/options-general.php	(revision 52607)
+++ src/wp-admin/options-general.php	(working copy)
@@ -66,9 +66,17 @@
 <td><input name="blogname" type="text" id="blogname" value="<?php form_option( 'blogname' ); ?>" class="regular-text" /></td>
 </tr>
 
+<?php
+	/* translators: Site tagline. */
+	$sample_tagline = __( 'Just another WordPress site' );
+	if ( is_multisite() ) {
+		/* translators: %s: Network title. */
+		$sample_tagline = sprintf( __( 'Just another %s site' ), get_network()->site_name );
+	}
+?>
 <tr>
 <th scope="row"><label for="blogdescription"><?php _e( 'Tagline' ); ?></label></th>
-<td><input name="blogdescription" type="text" id="blogdescription" aria-describedby="tagline-description" value="<?php form_option( 'blogdescription' ); ?>" class="regular-text" />
+<td><input name="blogdescription" type="text" id="blogdescription" aria-describedby="tagline-description" value="<?php form_option( 'blogdescription' ); ?>" class="regular-text" placeholder="<?php echo $sample_tagline; ?>" />
 <p class="description" id="tagline-description"><?php _e( 'In a few words, explain what this site is about.' ); ?></p></td>
 </tr>