Creating AJAX websites based on anchor navigation | yensdesign - Tutorials, Web Design and Coding
http://yensdesign.com/2008/11/creating-ajax-websites-based-on-anchor-navigation/

In this tutorial we will see how to create an AJAX website without lose the reference to the URL. What is that not lose the reference? If you have created some full AJAX website you have realized when you change the web content, the URL is not updated, so, the URL reference is lost. Services like Gmail uses it to increase the navigation’s user experience.