eWeek has an interesting article, Microsoft Office 2010 Debuts, Challenges Google Apps, about Microsoft's plans to offer Office 2010 as a free service to Microsoft Live subscribers.
In a step that demonstrates the rising primacy of applications that run via a Web-based interface, even versions of Office 2010 running from an on-premises data center will be made accessible through the browser...
Realizing that the future of IT may lie in the cloud, Microsoft has been moving away from its desktop-centered comfort zone to a more aggressive Web-based stance. Also at the Worldwide Partner Conference, Microsoft plans to announce Silverlight 3, the newest version of its RIA (rich Internet application) technology, which the company said will allow it to challenge Adobe and to provide, through new features such as enhanced video performance and support for various applications, a platform for its own browser-based initiatives.
Personally, I feel a loyalty to the desktop versions of Office. It makes sense to me to take advantage of innovations in client hardware. On the other hand, I can see the collaboration that web-based apps can facilitate. I like the idea of collaborating on a document in real time, where permissions can be managed on a granular level - like "Bobby and Sue can edit this web-based document, but the rest of the accounting group can only read it." I think in the near future, most documents, whether entirely web-based or file based, will be aware of who is doing what.