simple_login.php

<?php
// $Id$

/**
* @file
* Outputs block with simple links to login / logout.
*/

/** 
* Implementation of hook_block_info()
*/
function simple_login_block_info() {
    $blocks['simple_login'] = array (
        'info' => t('User logout / login links'),
        'status' => true,
        'region' => 'header',
        'weight' => 0,
        'visibility' => 1,
        'cache' =>  DRUPAL_CACHE_PER_USER,
    );    
    return $blocks;
}

/** 
* Implementation of hook_block_view()
*/
function simple_login_block_view($delta = '') {
    switch($delta) {
        case 'simple_login':
            $block['subject'] = '';
            $block['content'] = simple_login_contents();
            return $block;
            break;
    }
}

function simple_login_contents() {
    if (user_is_logged_in()){
        global $user; 
        $output = theme('username', array('account'=> $user)) . ' | ' . l('Log out', 'user/logout');

    } else {
        $output = l('Login', 'user') . ' | '. l('Create Account','user/register');
    }
    return $output;
}