//if you happen to have php 5.2.0 or higher you can use the standard json_encode() / json_decode() functions that are //way faster (coded in c, like 100 - 200 times faster)
//if you want to keep it portable in case, then try something like this:

if (!function_exists('json_encode')){ 
//now its portable to php ver. < 5.2.0 where you would otherwise have to install the php-json c-extension first
    include('JSON.php');
    $json = new Services_JSON();
    function json_encode($value){
        global $json;
        return $json->encode($value);
    }
    function json_decode($value){
        global $json;
        return $json->decode($value);
    }
}

// then just use the standard functions json_encode() / json_decode()