There seems to be a number of questions and misunderstandings around the license for the schemas and what people are allowed to do with the files. I’m not a lawyer, so I don’t want to try to interpret the license for you, but there is a pretty good FAQ up on the Office XML site. There is also an official site that talks all about the license: http://www.microsoft.com/office/xml/licenseoverview.mspx

Here are a couple interesting parts I pulled out from the FAQ (http://www.microsoft.com/Office/xml/faq.mspx) that might help out a bit:

Q.   If Microsoft obtains a patent for the Office 2003 XML Reference Schemas, does that in any way affect the royalty-free license?

A.   No, the license is unaffected. Under the patent license for the Office 2003 XML Reference Schemas, Microsoft offers royalty-free rights both to its issued patents and patents that may be issued in the future.

Q.   The patent license associated with the Office 2003 XML Reference Schemas states that "Microsoft may have patents and/or patent applications that are necessary for you to license in order to make, sell, or distribute software programs that read or write files that comply with the Microsoft specifications for the Office Schemas." What does this statement mean and to what specific patents and/or patent applications does this statement relate?

A.  As an industry leader in the design and development of innovative computer technology, Microsoft has made a significant investment in research and development (R&D). With an annual budget of nearly $7 billion, Microsoft's R&D commitment is among the highest of the world's major technology providers, both on an absolute basis and as a percentage of sales. Like other major technology providers, Microsoft routinely applies to governments around the world to obtain patents on our inventions. A patent establishes ownership of an invention, enabling the patent owner to benefit commercially from investments in innovation. A patent is granted if government patent examiners conclude that an invention is a true innovation compared with existing technology. Microsoft has been awarded thousands of United States patents, and our worldwide portfolio continues to grow.

Under the patent license for the Office 2003 XML Reference Schemas, Microsoft offers royalty-free rights both to its issued patents and patents that may be issued in the future as an outcome of the patent process. To learn more about Microsoft's intellectual property policy and to find links to government patent offices, we encourage you to learn more about Microsoft Intellectual Property at the Microsoft Web site.

We have chosen a simple and straightforward licensing approach that should appeal to a wide variety of potential licensees because it broadly covers all applicable patents and patent applications instead of only those that are enumerated.

I hope that helps out a bit. This isn't really a topic that I'm qualified to answer a lot of questions on, but please feel free to post comments. I'll at least try to dig up the right information.