Index: wp-admin/includes/class-wp-ms-users-list-table.php
===================================================================
--- wp-admin/includes/class-wp-ms-users-list-table.php	(revision 18667)
+++ wp-admin/includes/class-wp-ms-users-list-table.php	(working copy)
@@ -111,6 +111,7 @@
 	function get_columns() {
 		$users_columns = array(
 			'cb'         => '<input type="checkbox" />',
+			'id'         => __( 'ID' ),
 			'username'   => __( 'Username' ),
 			'name'       => __( 'Name' ),
 			'email'      => __( 'E-mail' ),
@@ -169,7 +170,8 @@
 						</th>
 					<?php
 					break;
-
+					case 'id':
+						echo "<td $attributes>$user->ID</td>";
 					case 'username':
 						$avatar	= get_avatar( $user->user_email, 32 );
 						if ( get_current_user_id() == $user->ID ) {
Index: wp-admin/includes/class-wp-ms-sites-list-table.php
===================================================================
--- wp-admin/includes/class-wp-ms-sites-list-table.php	(revision 18667)
+++ wp-admin/includes/class-wp-ms-sites-list-table.php	(working copy)
@@ -146,6 +146,7 @@
 		$blogname_columns = ( is_subdomain_install() ) ? __( 'Domain' ) : __( 'Path' );
 		$sites_columns = array(
 			'cb'          => '<input type="checkbox" />',
+			'id'          => __( 'ID' ),
 			'blogname'    => $blogname_columns,
 			'lastupdated' => __( 'Last Updated' ),
 			'registered'  => _x( 'Registered', 'site' ),