[bartonfink]

I may be talking out of my ass here, but isn't OO-XML and whatever Microsoft calls their new Office format exactly that?

[tptacek]

You're right, I forgot about the "proprietary" document formats that got transformed into "open" (heh) XML formats. Good point. Thanks!

[ianburrell]

Both OO-XML and ODF are XML based. They both put the main XML document in a ZIP archive along with metadata and other resources.