This code helps you to track on a Magento Store visitors and the conversions using the Perfect Audience service.

Perfect Audience: Magento Tracking Code

/*
    This code should be inserted to the bottom of this file: /app/design/frontend/default/default/template/page/html/footer.phtml
    Make sure to update your perfect audience tracking info (line 34).
    Tested with Magento 1.9.0.1
    Thanks to Sam327
*/

    <!-- Start of Perfect Audience Script -->
    <script type="text/javascript">
        (function() {
            window._pa = window._pa || {};
            if(document.location.href.indexOf('checkout/onepage/success') != -1) {
                <?php
                    $_tmp_amount = 0.00;
                    $product_id = "";
                    $lastOrderId = Mage::getSingleton('checkout/session')->getLastRealOrderId();
                    if($lastOrderId) {
                        $_tmp_amount = Mage::getModel('sales/order')->loadByIncrementId($lastOrderId)->getBaseGrandTotal();
                    }
                    if(Mage::registry('current_product')){
                        $product_id = Mage::registry('current_product')->getSku();
                    }
                ?>
                _pa.orderId = "<?php echo $lastOrderId; ?>";
                _pa.revenue = "<?php echo $_tmp_amount; ?>";
            }
            _pa.productId = "<?php echo $product_id; ?>";
            var pa = document.createElement('script'); pa.type = 'text/javascript'; pa.async = true;
            pa.src = ('https:' == document.location.protocol ? 'https:' : 'http:') + "//tag.perfectaudience.com/serve/542e77d51230da945700000d.js";
            var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(pa, s);
        })();
    </script>
    <!-- End of Perfect Audience Script -->

footer.phtml is cached (if you have caching enabled) so you can't put the code in there. I ended up creating a block containing the PA code and calling it via the local.xml file and disabling the cache on just that block.

anthonycreek is correct. You need to disable caching in this specific block, else it wont work.