Chris_Pratley's OneNote WebLog : OneNote 12 - Working as a team with shared notebooks: "Recently I've had some mail from various OneNote users telling me that they are using OneNote for team work - shared sections and folders of notes which every member of the team can read and contribute to, and of course search. I've also been reading blogs like this one. I like this post because sbreck describes exactly the type of scenario we are targeting OneNote 12 at. Of course, he is trying to do it with OneNote 2003, so he has a few issues. It works, but it runs into limits. OneNote 12 has had significant work done to make it a breeze to work in small to medium groups effectively and quickly."
Detailed overview of sharing and offline capabilities planned for OneNote 12. I think Chris Pratley and Ray Ozzie still need to spend some time together, however, as Chris appears to have some incorrect assumptions about Groove.
Update/clarification: if Chris was referring exclusively to the way people routinely use OneNote in conjunction with Groove (with GFS), his summary is accurate. Groove is definitely not file-based at its core, however.