Did you know that default file format for the next version of its Office Suite would be XML?  The old, binary format will still be available, but the default will now be Open XML.

The Office Open XML format is public and royalty-free, and the XML-formatted documents can be read and processed with any XML-processing language or tool. The Office output will be compressed by zipping the XML, which is expected to result in 75% smaller than raw XML.

Source:  http://www.devx.com/xml/Article/28298