It is interesting to me that Office 2007 Metro formats can be broken down as a ZIP file. To see this in action, you can pick an Office 2007 Metro file, such as XLSX and DOCX, and rename its extension with ZIP. Then open the renamed file with WINZIP. You will see that Office 2007 content is laid out neatly in a ZIP. Check out this sample picture.
Let me illustrate a picture from http://www.devx.com/MicrosoftISV/Article/34934