Keeping a business running smoothly depends a lot on communication, so I can see how having the ability to leave notes for other departments would be useful. There currently isn't an integrated feature for leaving notes for other users, but you may be able to make use of the memo section on transactions as a workaround. That way, you can leave any necessary details that another department may need.
Reports also have a comments feature that you can make use of. Simply follow these steps.
Run the report you'd like to add comments to.
At the top of the report window, click the Comment On Report button.
Add your comments by clicking the icon next to a line.
Hit Save for the comment.
Click Save at the top of the window to save the report with its comments.
The function you describe is essentially useless. It enables you to leave a note on a specific line of a report (marks the line with an identifying number and the corresponding Note is displayed at the bottom of the report. The Report must be memorized or the Notes are not saved. Everyone must have access to the report in QB in order to view a note or to leave a note for the next person.
I hear what you're saying and know it isn't a perfect solution. As always, if other users have solutions that have worked for them, I welcome them to chime in and share. We're all here to help each other out so we can get the most out of using the program. :)