Has anyone here had success with the conversion pixel for Facebook tracking? Been trying to install the pixel but it doesn't seem to work. Facebook suggests we place their code in the <head> section, but does it really have to be there?

Their code is:

<!-- Facebook Conversion Code for Checkout -->
<script>(function() {
  var _fbq = window._fbq || (window._fbq = []);
  if (!_fbq.loaded) {
    var fbds = document.createElement('script');
    fbds.async = true;
    fbds.src = '//connect.facebook.net/en_US/fbds.js';
    var s = document.getElementsByTagName('script')[0];
    s.parentNode.insertBefore(fbds, s);
    _fbq.loaded = true;
window._fbq = window._fbq || [];
window._fbq.push(['track', '6013608501246', {'value':'0.00','currency':'USD'}]);
<noscript><img height="1" width="1" alt="" style="display:none" src="https://www.facebook.com/tr?ev=6013608501246&amp;cd[value]=0.00&amp;cd[currency]=USD&amp;noscript=1" /></noscript>
FB says we need to assign a value to the 'value' field, and points out that we can "dynamically update this value using a server-side variable (ex: you can insert shopping cart value into the value field of the pixel that uses the checkout pixel)."

Does that mean I can input array Order[2] in the value field like so:
window._fbq.push(['track', '6013608501246', {'value':'Order[2]','currency':'USD'}]);
Any help/stories/experience would be appreciated.