In the world of ‘software-as-a-service’, the interface to your world is a web browser. It doesn’t matter what brand of operating system your computer is running or what brand of browser you prefer. As long as they are modern and adhere to today’s standards, which is what you get from Windows, Linux, Mac OS X, IE 7, Firefox, Opera and others, you have a computer that is powerful enough to run a web based program, or software as a service.
For years there have been competitors to Microsoft Office, none of which have truly had the traction necessary to make any real dent in Office revenue. Sure, OpenOffice is at version 2.0 and has both consumer and corporate support.