http://ie.microsoft.com/testdrive/HTML5/DOMContentLoaded/Default.html
The DOMContentLoaded event fires when parsing of the current page is complete; the load event fires when all files have finished loading from all resources, including ads and images. DOMContentLoaded is a great event to use to hookup UI functionality to complex web pages.
http://jsperf.com/onload-vs-domcontentloaded
http://ablogaboutcode.com/2011/06/14/how-javascript-loading-works-domcontentloaded-and-onload/