If you save an Office 2007 document in its default format, and then review the XML files stored in the .docx (zip) container, you might conclude that Office Open XML is complex. And it can be, because it has to be able to represent everything in that Office document. But it doesn't have to be. In this Hello World screencast, Office program manager Brian Jones shows how to construct a minimal Word 2007 file from the ground up.
You can do the same kind of thing in Excel 2007. In a three-part series on his blog -- part 1, part 2, and part 3 -- Brian shows how little XML is required to create a spreadsheet, populate it with data, add functions that operate on the data, and apply formatting.
Because it's now possible to create Office 2007 documents in these ways, using standard XML-oriented tools, developers on all platforms can now much more easily make information in other formats available to users of Office 2007.