And for those 'deskless' workers who only need occasional access to e-mail and related services, Microsoft is offering at just $36 a year.

Many of these measures will cut mightily into Office's profitability. But they may also stanch enterprise customer defections in the near-term, said DeGroot.

Still, DeGroot warned that the inertia propelling Office upgrades forward is "losing a lot of steam" among both smaller companies as well as "companies that started out bigger but need to find ways to reduce staff and overhead." And as "the online products get spiffier interfaces and more features, Microsoft could find it harder to pull these companies back into the Office orbit," he said.