ODF vs OOXML
ODF and OOXML are open document formats that are meant to be used in cross-platform and cross-suite environments. ISO voted in ODF as an international document standard in 2006. ISO also voted in OOXML as an international document standard in 2008. There have been many complaints, however, that the process to vote in OOXML was done haphazardly.
The discussions around Open XML and ODF are a proxy for product competition in the marketplace. Ultimately, this attention and focus on the needs of those who use office productivity software is a good thing for all concerned, but the attention being paid relates back to the commercial opportunities for MS Office, IBM’s Workplace (Open Client), and OpenOffice commercial offerings from Sun and others. For us, the move to an XML-based file format is an important aspect of Office 2007.— Tom Robertson, General Manager of Interoperability and Standards, Microsoft , Microsoft: Why the ODF vs. OOXML battle matters
Open Office and KOffice both support the ODF format. Novell is planning on introducing OOXML support in Open Office in the future. Microsoft recently announced ODF support in Microsoft Office (for Windows only).
Microsoft Office 2007 and newer for Windows support the OOXML format. No Mac version of Microsoft Office has ever included ODF support. Microsoft has released a Compatibility Pack that allows OOXML in older version of Office. 
ODF is designed by Open Office.
OOXML is designed by Microsoft.
Both ODF and OOXML are XML standards for documents. The files they generate are compressed XML documents.
ODF "only locks in a very significant amount of functionality, rather than complete uniformity (as OOXML strives to achieve)."