While I agree that this is an interesting, useful, and novel use of wordpress, I don't see any major advantages of using this compared to something like Evernote, Google Notebook, or (the upcoming) OneNote Online. I'm not sure how much granularity these give you in terms of access control, but Google Notebook has sharing of at the notebook level, publishing to public web pages, etc. It also allows commenting and tagging on notebook entries.

Google Notebook, however, has the disadvantages of requiring a google account, and (I believe) being dropped from active development. Also, I suppose WP has the advantage of greater customization.