Rick Jelliffe has another informative poston OpenDocument format vs Office Open XML.
I have left a comment there questioning some of the detail, but I like the conclusion:
Which is why I think it is better to consider the bottom line: can all the information be round-tripped, even if with effort? That is the information that anyone with archiving and data conversion requirements should be considering more than initial eye-rolling, however understandable, I think
Rick is saying that the important thing is interoperability, both with current tools and with the future.
To which I add, if you care about document processing now and into the future and you're working with word processing documents use styles to mark the bits of your document that have structural and semantic significance. If you use styles then the task of converting from one format to another becomes much easier; you can forget all the discussion about wrapper elements and work from the style names (even if they happen to be a bit obfuscated by the file format as in ODF).
I have noted before that we have already achieved some of this interoperability with the ICE template, and an alternative implementation by Ian Barnes.