The next Microsoft Office (12) is going to use XML as it’s default file format. The old binary .doc, .xls and .ppt file formats will be replaced with new file technology based on XML and zip compression.
Brian Jones backgrounds the history of Office file formats and why this change is being made. There are some interesting examples on assembling documents from “fragments” and auditing masses of files which could be very useful for CAD documentation.
Brian Jones: Office XML Formats
Some background information on the reasons we have moved to an XML format as the default in Office "12"