Ayer comentaba sobre la clase PHP para enviar canciones a last.fm. Bueno dado que lo voy a utilizar desde CakePHP lo más lógico era construir un componente, y gracias al HttpSocket de CakePHP el código se redujo bastante. Aquí les dejo el código para usarlo libremente (MIT License)

< ?php
/**
 * last.fm component for songs submissions
 * Send songs to last.fm using cakephp
 *
 *
 * PHP versions 4 and 5
 *
 * Copyright 2008, Pablo Viojo
 *
 * Licensed under The MIT License
 * Redistributions of files must retain the above copyright notice.
 *
 * @filesource
 * @copyright			Copyright 2008, Pablo Viojo (http://pviojo.net)
 * @link						http://projects.pviojo.net/lastfm
 * @version				0.1.1
 * @lastmodified		2008-07-26
 * @license					http://www.opensource.org/licenses/mit-license.php The MIT License
 *
 * Usage sample:
 * 

 if($this->Lastfm->connect($user, $password)){
	if(
		$this->Lastfm->submit(
			array(
				'artist'=>'Artist',
				'title'=>'Song Name',
				'album'=>'Album nane',
				'duration'=>duration(secs)
			)
		)
	 ){
		// ...submission success
  	}
  }

 *
 */	

if (!defined('LASTFM_CONNECTED')){
	define ('LASTFM_CONNECTED', 'OK');
}
if (!defined('LASTFM_ERROR')){
	define ('LASTFM_ERROR', 'ERROR');
}

App::import('core','HttpSocket');

class LastfmComponent extends Object {

/**
 * Constructor.
 */
	function startup(&$controller) {
		$this->controller = $controller;

		$this->clientId = "tst";
		$this->clientVer = "1.0";

		$this->socket = new HttpSocket();

	}

/**
 * Connects to lastfm using user and password
 */
	function connect($user, $password){
		$this->user = $user;
		$this->password = $password;
		return $this->_handShake();

	}
/**
 * Returns true if connected to last.fm
 *
 * @return boolean Connection Status
 * @access public
 */
 	function isConnected(){
		if ($this->status==LASTFM_CONNECTED){
			return true;
		}

		return false;
	}
/**
 * Performs a handshake
 *
 * @return Status (LASTFM_CONNECTED on success, LASTFM_ERROR otherwise)
 * @access private
 */
	function _handShake(){

		$this->status = false;

		$timestamp = time();
		$auth = md5(md5($this->password) . $timestamp);

		$url = "http://post.audioscrobbler.com/?hs=true&p=1.2.1&c=" . $this->clientId . "&v=" . $this->clientVer . "&u=" . $this->user . "&t=" . $timestamp . "&a=" . $auth ;
		$rsp = $this->_execute($url,  array('username'=>$this->user, 'password'=>$this->password));
		if ($rsp){
			$rsp = split("\n",$rsp);
			$this->status = $rsp[0];
			switch($this->status){
				case "OK":
					$this->status = LASTFM_CONNECTED;
					$this->sessionId = $rsp[1];
					$this->urls['nowPlaying'] = $rsp[2];
					$this->urls['submission'] = $rsp[3];
					break;
				default:
					$this->status = LASTFM_ERROR;
					$this->sessionId = null;
					break;
			}
		}
		return $this->status ;
	}

/**
 * Submit a song to last.fm
 * @param array $song array ("artist", "title", "duration", "album"[, "start"] )
 * @return boolean Submission Status
 * @access public
 */
	function submit($song){

		$timestamp = time();
		$auth = md5(md5($this->password) . $timestamp);

		$data = array(
			"s"=>$this->sessionId,
			"a[0]"=>$song['artist'],
			"t[0]"=>$song['title'],
			"i[0]"=>(isset($song['start'])?$song['start']:time()),
			"o[0]"=>"P",
			"r[0]"=>"",
			"l[0]"=>$song['duration'],
			"b[0]"=>$song['album'],
			"n[0]"=>"",
			"m[0]"=>""
		);

		$url = $this->urls['submission'];
		$rsp = $this->_execute($url,  array('username'=>$this->user, 'password'=>$this->password), 'POST', $data);
		switch(trim($rsp)){
			case "OK":
				return true;
				break;
			default:
				return false;
		}
	}

/**
 * Execute a request
 * @access private
 */
	function _execute($url, $auth = null, $method = 'GET', $data = null){

		$request = array(
			'method' => $method,
			'uri' => $url
		);

		if ($auth){
			$request = am(
				$request,
				array(
					'auth' => array(
						'method' => 'basic',
						'user' => $auth["username"],
						'pass' => $auth["password"]
					)
				)
			);
		}

		if (strtoupper($method)=="POST"){
			if ($data){
				foreach($data as $key=>$value ) {
					$postData[$key] = $value;
				}
				$request['body'] = $postData;
			}
		}

		$output = $this->socket->request($request);
		return $output;

	}

}