"One of Microsoft's most important principles has been to control standards, don't let others set standards for you. When that has happened, they have regretted it," DeGroot said. "They might succeed in marginalizing ODF, but they also give away any clout in future ODF discussions and risk the possibility that customers who care deeply about format longevity and longterm document accessibility will go with ODF rather than Office XML."

DeGroot said the move is a "half-way measure" by Microsoft, who he says "would do a whole lot better if they would just bite the bullet and do this themselves. If they did, anyone who bought Office would have it, and Microsoft would support it. In my view, they're setting themselves up for a major headache later on."

But other observers praised Microsoft's move to dip its toe into open-source waters it has long publicly disdained. "I welcome Microsoft into the OpenDocument environment," said Douglas Johnson, corporate standards program manager for Sun. "Sometimes zebras get new stripes."