I've been playing around with Sharepoint Team Services as a way to keep my OneNote sections synchronized across multiple machines (my tablet, home pc, and work pc).
I was hoping for the same experience as I get with Exchange - I have multiple ways in to access the same data, and it is all done seamlessly for me. There are couple of problems I've noticed in the day or two I've had this running that may, unfortunately, make this impractical for now.
The integration is simply adding a .URL shortcut to the Notebook folder. Under the hoods, it looks like OneNote fetches the file and saves it to the temp cache directory. Unfortunately, there's still no "local copy" of the file - if I'm disconnected, I have to save the file to another location and then reupload at a later date. I also can't get my notes when I'm offline.
Not surprisingly, .ONE files with Ink are significantly larger than ones with all text, even with pressure sensitivity turned off. (When I say much larger, I mean an order of magnitude: a section with less than 20 pages, many of which are a single screen or less, is hovering around the 2MB mark. By comparison, a text-only section of similar size is only 380k. Converting the original Ink section entirely to text cuts about 30%, but nowhere near as small as if the section never had Ink.)
These two issues, considering I originally planned on using this extensively from the tablet, makes the process dreadful.
In my mind, the ideal situation is having a local .ONE file with metadata associated about the original document workspace. When offline, it acts like any other local file. When I connect, however, it then turns around and does the update. (And please, ONLY the updates - the current process requires me to upload the entire file if I want to work offline!).
I think the nature of OneNote makes this "offline mode" more important than other Office applications. OneNote already goes to great lengths to hide the "complexity" of the underlying files, handling a lot of this stuff automagically for the user. As a note-taking application, it becomes more intrusive to check out a notebook, add something to it, and check it back in, whereas that might be as much of an issue in, say, Word.