I've had a few folks ask this question so I figured I'd just quickly call it out. As we've been discussing, we will have new XML formats for Office '12' in Word, PowerPoint, and Excel. The new Word XML format is really similar to the XML format in Word 2003. The Excel format is actually a more significant change (as you can see if you look at the preview of the schemas posted last week)

While we are moving to new formats, we will continue to support the XML formats from Office 2003 as well. So, if you've built solutions on top of those formats, you can either migrate those into the new formats, or just continue to use the existing formats. One big advantage of using the new XML formats is that we are providing updates for Office 2000, XP, and 2003 users that gives them full read/write support for the new XML formats.