Check out this link:
http://google.blogspot.com/view/timeslide
And click on the post and as you can see the URL is changing but without a # or something like that, It changes like the page would load normally, but the content changes just like it would be built with AJAX.
This happens with Chrome 10 with the latest stable version, but for Firefox 3.6 it uses the old way with the hash :)
How is this possible, is this a new HTML5 feature or what?
pushState: