I learned this afternoon from Gray Knowlton, that a commenter on Brian's blog had linked to a couple of interesting items over on IBM.com. It looks like IBM has at least a couple of products that are now supporting the Open XML formats.
The WebSphere Portal for z/OS has some information about how to set up Document Conversion Services for Open XML documents:
And DB2 Content Manager V8.4 supports Open XML as well:
With so many IBM people involved in the DIS 29500 standards process worldwide, it's good to see that they're putting their growing Open XML expertise to work!