Index: wp-admin/includes/class-wp-media-list-table.php
===================================================================
--- wp-admin/includes/class-wp-media-list-table.php	(revision 20489)
+++ wp-admin/includes/class-wp-media-list-table.php	(working copy)
@@ -130,8 +130,8 @@
 		$posts_columns['icon'] = '';
 		/* translators: column name */
 		$posts_columns['title'] = _x( 'File', 'column name' );
-		$posts_columns['author'] = __( 'Author' );
-		//$posts_columns['tags'] = _x( 'Tags', 'column name' );
+		if ( _get_user_count() > 1 )
+			$posts_columns['author'] = __( 'Author' );
 		/* translators: column name */
 		if ( !$this->detached ) {
 			$posts_columns['parent'] = _x( 'Attached to', 'column name' );
Index: wp-admin/includes/class-wp-posts-list-table.php
===================================================================
--- wp-admin/includes/class-wp-posts-list-table.php	(revision 20489)
+++ wp-admin/includes/class-wp-posts-list-table.php	(working copy)
@@ -266,7 +266,8 @@
 		/* translators: manage posts column name */
 		$posts_columns['title'] = _x( 'Title', 'column name' );
 
-		if ( post_type_supports( $post_type, 'author' ) )
+		$total_users = isset( $_POST['total_users'] ) ? (int) $_POST['total_users'] : _get_user_count();
+		if ( post_type_supports( $post_type, 'author' ) && $total_users > 1 )
 			$posts_columns['author'] = __( 'Author' );
 
 		if ( empty( $post_type ) || is_object_in_taxonomy( $post_type, 'category' ) )
@@ -1043,6 +1044,7 @@
 			} ?>
 			<input type="hidden" name="post_view" value="<?php echo esc_attr( $m ); ?>" />
 			<input type="hidden" name="screen" value="<?php echo esc_attr( $screen->id ); ?>" />
+			<input type="hidden" name="total_users" value="<?php echo esc_attr( _get_user_count() ); ?>" />
 			<span class="error" style="display:none"></span>
 			<br class="clear" />
 		</p>
Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 20489)
+++ wp-includes/functions.php	(working copy)
@@ -3693,3 +3693,21 @@
 	}
 }
 
+/**
+ * Retrieve the total number of users in the DB.
+ *
+ * @since 3.4.0
+ * @access private
+ *
+ * @return int Number of users.
+ */
+function _get_user_count() {
+	global $wpdb;
+
+	if ( ! $user_count = wp_cache_get( 'user_count', 'users' ) ) {
+		$user_count = $wpdb->get_var( "SELECT COUNT(*) FROM $wpdb->users" );
+		wp_cache_add( 'user_count', $user_count, 'users' );
+	}
+
+	return $user_count;
+}