Register users without confirmation

Well there is a function called wp_new_user_notification() which is pluggable you can alter it to stop user registration email:

if ( ! function_exists( 'wp_new_user_notification' ) ) {
    function wp_new_user_notification( $user_id, $plaintext_pass="" ) {
        return false; // because we don't need to send email.
    }
}