mymodule_fancystuffjson.php

<?php
function mymodule_menu() {
    $items['fancystuff/json/%'] = array(
        'access callback'   => true, // available to all
        'page callback'     => 'mymodule_fancystuff_object', // defined below
        'page arguments' => array(2),
        'delivery callback' => 'drupal_json_output' 
    );
    return $items;
}



function mymodule_fancystuff_object($userid) {
    return array('test'=>true,'dummy'=>array(0, 1, $userid));
}