Here is an excellent summary of the salient differences between the OpenDocument Format (ODF) and Microsoft’s Office Open XML format. I strongly recommend everyone considering OOXML/OpenXML take a look at it before either supporting it as an ISO standard or adopting it directly.
This is an example of buyer beware. I’m not sure how much more strongly one can make the case that ODF is, well, open, and OOXML/OpenXML is, well, Microsoft’s personal and private XML specification for its product. As I’ve said multiple times, Microsoft has every right in the universe to have its own formats, but that is different from making private, proprietary formats into international standards that no one else will be able to implement in their entirety.
If you want insurance for the future that you will not be locked into the whims and technical decisions of a single vendor protecting its products and marketshare, go with ODF. If you are just fine with the avoidable loss of your freedoms to choose from a range of applications and are willing to commit to a single vendor, go with OOXML. That is the real choice here, and I think (I hope) most people understand that. If you are not paying heed to the deep technical and market control issues with OOXML, then you are trivializing what is really happening here.
Don’t, because you’ll pay for the consequences for a long, long time. Don’t, because there is a real open, international document standard called ODF already in place that is being actively developed by a global community of experts. Don’t, because we’re all smart enough to see through the FUD and the fluff to recognize the lock-in play in OOXML that just happens to be wrapped in a standards disguise.