The new Word, Excel and PowerPoint formats will be designated as .docx, .xlsx and .pptx, respectively. Microsoft is referring to the family of new formats as "Microsoft Office Open XML Formats." Microsoft is committing to publish the forthcoming XML formats and make them available under the same royalty-free license under which the current Office 2003 file formats are.
Licensees will be able to integrate these formats into their servers, applications and business processes "without financial consideration to Microsoft," according to the Redmond software vendor.
For users of older versions of Office—specifically Office 2000, Office 2003 and Office XP—Microsoft will make available software downloads that will allow them to read, edit and save using the new file formats.
i believe this is a step towards the so called 'Metro' format that MS is proposing (metro is an XML - based formay in an atempt of MS to replace PDF -- its a portable, open document )
http://www.eweek.com/article2/0,1759,1822685,00.asp
RELATED Openoffice to use an XML file format in upcomming versions (hmm this was announced b4 ms announced are bills boys playin catchup??)
http://www.eweek.com/article2/0,1759,1819244,00.asp