Well, it was all the way back in March when we had the Office Developer's conference out here in Redmond. It was a lot of fun, as we actually had a track dedicated to the Open XML formats. There were three separate presentations and we were able to get into some pretty good details.
Now, almost 5 months later, we finally have the videos from the conference available online. They are all pretty raw, and definitely unedited, but I figured you might still be interested in taking a look. Here are the three file format talks if you are interested:
Another interesting talk was: Word 2007 XML Programmability: Data/View Separation and Rich Eventing for Custom XML Solutions - For those of you interested in learning more about content controls and custom XML mapping in Word, you should check out Tristan's talk. He talks about how to set up XML mappings, as well as the powerful additions made to the Object Model for content controls.