It would be handy to have some sort of "watch this notebook" or "watch this note" feature. Allow a business user to "watch" a note or notebook and be notified of any changes to a note or additions/changes to a notebook. Allow the user to select notification method: email or push notification... or even text message perhaps. There are many instances when collaborating where time is of the essence. A push notification letting "watchers" know that a change has been made to a note... or a change/addition (new note) has been made to a notebook would be very helpful.