Doug Mahugh, Office 2007 Technical Evangelist, has been digging into the details of the Office Open XML specs and blogs the spec's key concepts for developers.
In this post he covers “Packaging” of Office 2007 files and how the different parts are the chunks of content that make up the document.
 
The ability to develop your own .zip-files using the managed code creates lots of new opportunities for ISVs. Meanwhile I'm looking forward to Doug’s System.IO.Packaging API code examples to code these packages.