CNET has some good news for those who are write commercial applications that interoperate with Office and need to read and write Office files.
CNET reports that Microsoft has agreed to offer a royalty-free license of Office-related XML documents in perpetuity. Previously, Microsoft had acquired a patent over the use of Microsoft XML file formats, dampening whatever enthusiasm ISVs and customers may initially have had over relying on the Office's XML. This followed a pattern of Microsoft restricting or inconveniencing software vendors from interoperating with Office in attempt to protect its intellectual property (such as not allowing redistribution of icons, I mentioned in an earlier post).
There are still issues to the new openness. Most of Office's XML are only supported in Office 2003, such as Word's XML format (aka WordprocessingML), although most of the markup may be identical to the embedded XML stored in the round-trippable HTML formats, that Office introduced in Office 2000. Excel's XML (aka SpreadsheetML) is also supported in the previous version of Office, Office XP. (I had a hand in its development prior to leaving Microsoft.)
Why do I care? I am writing software that interoperates with Microsoft Word, and I found the task of reading complex formatting from Word's binary files (prohibitive for an initial version), although simply reading the text data is straightforward. Instead, I work with both RTF and HTML, which Word supports round-tripping to. If Word is also installed in the user's machine, I'll support reading and writing of DOC files by having Word convert the files to RTF through OLE automation. The XML support is nice to have, but it's only available in Word 2003.