Welcome the new "Office Open XML Formats" - Office 12 goes XML all the way!
So the secret is out on Office 12... which is great but a I was kind of expecting a Tech*Ed announcement for major impact as opposed to a week-before limited fanfare press release. Even if MS downplayed this a bit now, this really changes the landscape for Office in such a huge way. New default file formats based on XML and ZIP. Think about that... standards on standards, documented with full fidelity for all application features (unlike uh... Excel 2003).
Microsoft has really allowed an open environment for Office that many people never expected they would do. Also note that this also allows non-Office 12 users to take advantage of the new “12x” format equally as well. The format, which builds upon the recently announced Metro specification from MS for defining documents, offers so many cool things that I will point you at Joe Andreshak's blog post to find your reading material. Make sure you check out Brian Jones on Channel9 and his blog too. If you are a developer ... I highly encourage you to start looking at this System.IO.Packaging class from the WinFX SDK. It is going to be the keys to the document kingdom ;)
If you are at Tech*Ed next week, make sure to see Joe and Brian's session on the new format. I will be there no doubt (so say “hi”).... And if you are really bored, come see my talk on programming XML in “out-dated” Excel 2003 :\
(Post written in .docx - well... not really but soon ;)