I don't know. I very much like the idea and to couple it with HTML5 elements, like
<header>and
<footer>, but (although I've not read everything extensively) it doesn't seen to cover every kind of website (specifically the gambling ones I work on).
There is a casino tag, but that's for a location rather than a site. I could mark up the promos as an offer, but that's not really what it's for. I could mark them up as articles, but again it's not a great fit either. And again same with product.
I really only think it'll be useful for categorizing pages which may be shown on differing SERPs pages. Otherwise it doesn't seem to be a particularly good idea to use it as a big ranking factor when not all sites can use it.
Certain elements like 'mainContentOfPage' and 'mainImageOfPage' and 'signifcantLinks' may count (and are the sort of thing all sites can impliment) but for every tag to carry a weight... I'm not sure.
Of course I may just be trying to convince myself of this as implimenting these tags on dozens of sites is not going to be fun.
</footer>
</header>