It would be great to be able to add a note (to self, or to cleaners) to the booking calendar. For example "Stove repairman coming today", "Call maintenance", "Don't forget to call Joe", "Guest checking in early today", etc. Adding a note to a booking would not suffice, needs to be something that you see when you look at the monthly calendar or the ribbon. Of course, it should be something that doesn't block the date from being booked.
With the ability to restrict access to seeing it!