Can I use multisite functions in a single-site installation?

get_transient / set_transient example:

function my_get_user_count() {
    $usercount = get_transient('usercount');
    if (!$usercount) {
        $usercount = count_users();
        set_transient('usercount',$usercount,600); // ten mins
    }
    return $usercount;
}