HTML5 has a new tag,
Do popular search-engines ignore contents within such tag when they generate page summaries?
As far as i know, Google will not differentiate the tags as whatever they see in view source, they will consider them while indexing the page.
I did some search on Google and found this interesting discussion on Google product group. http://productforums.google.com/forum/#!topic/webmasters/NvB9f5n0saU
This post is bit old but you can find the solution you are looking for.