There is a new report out from Directions on Microsoft that discusses the new Open XML formats, and the impact on Office customers. It discusses the benefits that organizations will see from the formats, as well as some deployment recommendations. Here is a link: http://www.directionsonmicrosoft.com/sample/DOMIS/update/2007/01jan/0107nffio2.htm
I liked Rob's overview of the payoffs for Content Management, Public Sector:
The most important benefit of the new file formats will be for software developers and integrators who use Office as part of a larger solution. Because the Office XML formats are documented and accessible through standard APIs and tools, applications other than Office can do tasks such as generating documents from user input and extracting data from documents for business applications such as customer relationship management (CRM) systems. Microsoft itself could eventually benefit: the company's business applications (such as Dynamics CRM) could exploit the formats to extract information from Office documents or annotate them.
It's definitely the case that on top of all the solutions other folks can build, even within Microsoft we'll see other teams building solutions they couldn't have easily done before. The ability to generate or consume a rich Office documents in other applications is a huge shift for the market.