This is something really useful, thanks for the post. I would like to add some information :

This can be combined with asynchronous loading of javascript, where you can earn some seconds during loading. That’s what I use to display share buttons such as Facebook or Google+.

Let’s take a look at the code

// Google+ Tag
googleTag.type = ‘text/javascript’;
googleTag.async = true;
googleTag.src = ‘http://apis.google.com/js/plusone.js’;

var s = document.getElementsByTagName(‘script’)⁰;
s.parentNode.insertBefore(googleTag, s);

Have some fun !