I won't pass judgment on Microsoft's sincerity, although I find Allison's claims quite credible. Certainly I've had plenty to say about the OOXML standard in the past.
But I think that even with good faith and good engineering, interoperability in something as complex as an office suite may be unachievable. This ties in with a blog I wrote a few weeks ago titled Open Cloud Manifesto: about openness, standards, and the vitality of SMTP.
I suggested there that, to be successful, a standard has to be simple and deal with an extremely well-known problem. A fine comment by Rick Jelliffe talked about the importance of understanding layers and said that a standard works when companies aren't jockeying for competitive success on that layer.
All those considerations can be applied here. Not only is an office suite massive and overflowing with different components; it has to hook into a huge number of outside pieces in its environment: the file system, a database, multimedia programs, etc.
Although I support the standardization efforts around ODF, I wouldn't blame either the ODF standardization committee or Microsoft for a failure to interoperate. We're just going to have to live with a fuzz factor.