I think it's a bit of a stretch to say Facebook has embraced the Semantic Web, but they've become a bit more semantically oriented. This article from ReadWrite web examines Facebook's open graph. "Eeach web page can now become an 'object' in Facebook's social graph (which is Facebook's term for how people connect to each other in its network). This means that pages can be referenced and connected across social network user profiles, blog posts, search results, Facebook's News Feed, and more." the nice part is, other people (like me) can see the markup in these web pages, and use it for our own purposes, which is exactly what the open web is supposed to support (of course, Facebook will get mad at you if you start harvesting semantic data from their website, but that's another story). See also the W3C's response.