/app/code/core/Mage/Log/Model/Customer.php

<?php
/**
 * Magento
 *
 * NOTICE OF LICENSE
 *
 * This source file is subject to the Open Software License (OSL 3.0)
 * that is bundled with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://opensource.org/licenses/osl-3.0.php
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@magentocommerce.com so we can send you a copy immediately.
 *
 * DISCLAIMER
 *
 * Do not edit or add to this file if you wish to upgrade Magento to newer
 * versions in the future. If you wish to customize Magento for your
 * needs please refer to http://www.magentocommerce.com for more information.
 *
 * @category    Mage
 * @package     Mage_Log
 * @copyright   Copyright (c) 2010 Magento Inc. (http://www.magentocommerce.com)
 * @license     http://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
 */

/**
 * Customer log model
 *
 * @category   Mage
 * @package    Mage_Log
 * @author      Magento Core Team <core@magentocommerce.com>
 */
class Mage_Log_Model_Customer extends Mage_Core_Model_Abstract
{
    public function __construct()
    {
        parent::__construct();
        $this->_setResourceModel('log/customer');
    }

    public function load($customerId, $field=null)
    {
        $this->_getResource()->load($this, $customerId);
        return $this;
    }

    public function getLoginAtTimestamp()
    {
        if ($date = $this->getLoginAt()) {
            return strtotime($date);
        }
        return null;
    }
}