A new draft of Open XML came out on my birthday. 4081 pages of PDF, and very impressive for anyone who has worked on specification and standards. Two things stick out: first how horrible XML Schema fragments are when stuck inline to document structure; second, how the implementation-neutral tone of the introduction is at odds with the elements for various kinds of Active X embedded objects. I suspect people would be a lot more comfortable if the elements for Active X embedded objects were in a different namespace, and gathered into an appendix of some kind. Antiques and curios. It will be interesting to see what the extensibility strategy will be (it hasnt been released in this draft.)
On the technical merits, well actually I dont know if they matter much. I say potato. Exporting to HTML or XHTML gives people base-level interoperability for most documents, which neither ODF nor Open XML will challenge; at the high end the solution is exporting to XML using a domain-specific schema (e.g. S1000D for military & aerospace) and not ODF or Open XML at all; in the casual middle we will have ISO ODF available, perhaps as the interchange format of choice, as well as ISO Open XML (if it is accepted) for when you need to track MS Offices capabilities closely. I think there is substantial value in a standard XML format for MS Office documents even within organizations that will mandate ODF for interchange and archiving. The availability of the alternatives reduces the need for ODF or Open XML to be the one true interchange format.
Probably coming from the industrial publishing background biases me here: the need for dumbed down interchange formats is real sure enough, but the need for intricate close-to-the-metal feature-exposing typesetting feature access is also important for different contexts. Words binary formats and RTFs weaknesses have long held Microsofts applications back from being happily usable in serious industrial publishing systems (or, at least, have often held back the people who adopted them.)