Forgive my cynicism, but where are the edges in the Open Graph Protocol?
As far as I can tell Facebook's graph has two vertex types, people, and things. The edges go between people and things and between people and other people (i.e. friends).
Facebook rightfully requires authorization to access the other parts of the graph through their API (the data is private, after all), but what bothers me is that there's no way to describe a graph of your own, or share it with anyone else.
In more practical terms, in this supposed graph specification there's no way to link to an og:url from my homepage saying that I like that thing (or maybe dislike, or have any other connection to it).
As a producer of "things", if I tell those things' og:type to the internet, my customers can "Like" my og:type. And then I can contact those customers (apparently for free), and presumably later pay Facebook to tell their friends about that thing more often. And there are a few other perks.
I get that Facebook is just trying to run an advertisement business, but why sell it as some hippy Open thing? Sure, part of the data is open, but the real graphyness is in the hrefs, which are still proprietary.
Illustrating my point, they reinvent hCards with a new XML namespace, instead of supporting hCards in their system. People are even less likely to adopt microformats if in order to use them they must add redundant data formats to their pages. It's not about the data being open to everyone, it's about the data being open to Facebook.
 The semantic web's immense success notwithstanding.