Unlike previous versions of html and xhtm (differences W3C) where the code gave limited structure which was determined by the heading tags <h1> - <h6> tags, html5 (W3C) provides much more structure.
All of the layout tags for html5 are semantic elements that determine the structure of the page. Each tag describes the type of content and its relationship to other content. Whereas before you could use divs indiscriminately the new tags require that some thought is given to their content and placement. I would imagine this will become especially important in terms of compliance to section 508.
Some time ago Google did a study in which they focused on code elements that were used the most. Part of that study focused on the most commonly used id and class names.
The new html5 tags for layout closely correlates with the names that are already commonly used by most web designers. So its not going to be much of a leap to start using html5 tags for layout.
Finalized
Html5 is ongoing and W3C expects it to be finalized by July 2014. May 22, 2011 was the confirmed date for the “Last Call”.