This is a great move forward for Microsoft Office. It means you will be able to open any Office document and edit the tags, or an inserted image’s properties, or comments etc. programmatically if you want to, for instance. This will allow for some cool server side stuff.
The xml is wrapped up in a zip container so file sizes will be about 25% of the size of existing docs – and there will be an update for Office 2000, XP and 2003 to allow these versions of Office to use XML as their default file format.
This is not a very original move on Microsoft’s part as they are merely copying what OpenOffice has had for a long time. But then no-one ever accused Microsoft of being innovative. Where it is important, though, is that MS Office has a much larger install base so developers will now be able to more easily create interesting server side MS Office applications.
Mac users are not being left out either according to Rick Schaut although, how much of the pie they are getting is not entirely clear from his post.