It would come in handy every once in a while, I think. It wouldn't even have to be anything more than a blank text box that does nothing but save what you type in it.
Or if you want get fancy, objects could have a "notes" button that, when clicked, pops up a little note window. And the button could highlight if there's a note present. And James Earl Jones could come by your house and read them out loud for you.
Okay, maybe not that last part.