Improved page segmentation. Search engines are getting smarter and there are many reasons to believe that even now they are applying page segmentation. Basically, page segmentation means that a page is divided into several separate parts (i.e. main content, menus, headers, footers, links sections, etc.) and these parts are treated as separate entries. At present, there is no way for a Web master to tell search engines how to segment a page but this is bound to change in HTML 5.
A new <article> tag. The new <article> tag is probably the best addition from a SEO point of view. The <article> tag allows to mark separate entries in an online publication, such as a blog or a magazine. It is expected that when articles are marked with the <article> tag, this will make the HTML code cleaner because it will reduce the need to use <div> tags. Also, probably search engines will put more weight on the text inside the <article> tag as compared to the contents on the other parts of the page.