WordPress New Users added to Mailchimp

gistfile1.php

<?php 
/*
Plugin Name: Primux Mailchimp
Plugin URI: http://primux.dk/
Description: Add new users to a Mailchimp list
Version: 1.0
Author: Primux Media
Author URI: http://primux.dk/
*/

add_action( 'user_register', 'mux_mailchimp_add' );

function mux_mailchimp_add( $user_id ) {
	$user = get_user_by('id', $user_id);

	$apikey = '' // API Key
	$listid = '' // List ID

	// $merges = array('FNAME'=>'Dave', 'LNAME'=>'Gilmour'); // IF you want to add other fields

	$double_optin=false;
	$update_existing=false;
	$replace_interests=true;
	$send_welcome=false;
	$email_type = 'html';            
	$data = array(
	        'email_address' 	=> $user->user_email,
	        'apikey'			=> $apikey,
	        // 'merge_vars' 	=> $merges,
	        'id' 				=> $listid,
	        'double_optin' 		=> $double_optin,
	        'update_existing' 	=> $update_existing,
	        'replace_interests' => $replace_interests,
	        'send_welcome' 		=> $send_welcome,
	        'email_type' 		=> $email_type
	    );
	$payload = json_encode($data);
	 
	//replace us2 with your actual datacenter
	$submit_url = "http://us2.api.mailchimp.com/1.3/?method=listSubscribe";

	$feedback = wp_remote_post( $submit_url, array( 'body' => $payload ) );
}
?>