Track each step of the Magento onepage checkout in Google Analytics with this simple Javascript addition to [package]/[theme]/template/checkout/onepage.phtml just add it to the bottom of that file and follow up by configuring with Google Analytics goals

onepage.phtml

<script type="text/javascript">
  Checkout.prototype.gotoSection = Checkout.prototype.gotoSection.wrap(function(parentMethod, section, reloadProgressBlock) {

    // Call parent method.
    parentMethod(section, reloadProgressBlock);

    var _gaq = _gaq || [];

    try {
      // push current checkout section to google analytics if available.
      _gaq.push(['_trackPageview', '<?php echo $this->getUrl('checkout/onepage'); ?>' + section + '/']);
    } catch(err) {
      // silent fail.
    }
  });
</script>