Developer on the IE team focusing on AJAX features for IE8. One of the AJAX improvements we adopted in IE8 from HTML5 is AJAX page navigations. In IE8 mode, we provide support for script to update the travel log components (for e.g. back/forward buttons, address bar) to reflect client-side updates to documents. This allows a better user experience where users can navigate back and forth without messing the AJAX application state.
For more information regarding the feature and sample code, refer to the Internet Explorer MIX08 Hands-on Labs for AJAX and IE8 Beta 1 for Developers. For an example of how this can be used to hook navigation in Silverlight (with sample code!), see Michael Scherotter’s blog posts titled How IE8 Enables Silverlight Deep Linking and Browser Back/Forward Navigation and IE8 Forward/Back in a Silverlight 2 (Beta 2) Application for further details.