For excellent coverage of the issue visit these two very well laid out posts by Greg Laden in 2007 when microsoft released the .docx file format. (Yes, I am a mac user and an Open Source software user. I do run a virtual machine with windows on it but use exclusively open source office software.)
Additionally, the following points are from the website <NO> OOXML, which has a petition where you sign up to protest against the the use of this broken attempt at a standard
- There is already a standard ISO26300 named Open Document Format (ODF): a dual standard adds costs, uncertainty and confusion to industry, government and citizens;
- There is no provable implementation of the OOXML specification: Microsoft Office 2007 produces a special version of OOXML, not a file format which complies with the OOXML specification;
- There is information missing from the specification document, for example how to do a autoSpaceLikeWord95 or useWord97LineBreakRules;
- More than 10% of the examples mentioned in the proposed standard do not validate as XML;
- There is no guarantee that anybody can write software that fully or partially implements the OOXML specification without being liable to patent lawsuits or patent license fees by Microsoft;
- This format conflicts with existing ISO standards, such as ISO 8601 (Representation of dates and times), ISO 639 (Codes for the Representation of Names and Languages) or ISO/IEC 10118-3 (cryptographic hash);
- There is a bug in the spreadsheet file format which forbids any date before the year 1900: such bugs affect the OOXML specification as well as software applications like Microsoft Excel 2000, XP, 2003 and 2007.
- This standard proposal was not created by bringing together the experience and expertise of all interested parties (such as the producers, sellers, buyers, users and regulators), but by Microsoft alone.
Anyone have more to add to the list?