Microsoft announced that it is ready to change to make its tools more interoperable, or as it says expand the interoperability. Is Microsoft serious about open source interoperability? I think it is yet another announcement to keep the buzz alive, and it is not only me who thinks so. Like Alan says, the timing is enough to not let others dwell on it enough.
For me, commitment to interoperability requires commitment to standards. Microsoft has still not been able to get a browser comply to the standards. Neither is OOXML serving as an open standard. Most of Microsoft’s activities have been to lock the users in their tools through closed standards. Though this might earn them money, it will not go a long way if the users are at a disadvantage. If Microsoft wants to be serious about interoperability they need to talk standards, the standard way, before anything else.