I really only need the mlid and title text for the first level below a certain menu item. Here's what I'm doing at the moment. (It works, but I suspect there may be a more drupal-y way.):

/**
 * Get all the children menu items below 'Style Guide' and put them in this format:
 * $menu_items[mlid] = 'menu-title'
 * @return array
 */
function mymod_get_menu_items() {
    $tree = menu_tree_all_data('primary-links');
    $branches = $tree['49952 Parent Item 579']['below']; // had to dig for that ugly key
    $menu_items = array();
    foreach ($branches as $menu_item) {
        $menu_items[$menu_item['link']['mlid']] = $menu_item['link']['title'];
    }
    return $menu_items;
}

Is there?