HTML5 and Microdata Tagging SEO
As for microdata, its main goal is to add more context to data presented on the web. An example would be invisible tags around an address that lets Google and your browser know that the first line is the street address, the second is the room number and the third line contains the city/state/zip codes. This is all well and good as it will help users searching your site find tagged content more easily (either via search of the browser itself; and even browser wise only Oracle currently supports them currently). However, Google has stated that this is a content/semantic addition to their search only and will not have any affect on page rank. It also means for cases where the tags are not being automatically generated, when entering your content you would have to manually tag items, which can be a chore, especially if you are getting nitty gritty into details.
So the gist of all this boils down to: We do use HTML5 when we feel it fits the project and will continue to expand its use as it gains traction from all of the major browsers. For microdata tagging, we take more of a "if we think it's a good fit for the client's data" approach. But the takeaway from all of this is that HTML5 and microdata tagging is not the answer to better search engine optimization. The true answer to better search engine optimization will always be better content.