Many (if not all) of the developers that I work with including myself keep a notepad (electronic or otherwise) for each project. I imagine it would be convenient to have a tab that is simply a note area. A simple text editor with no styling for me to make a note to myself. Something that wouldn't get shared with the source that was a piece of the project.

I use to maintain a notepad for each and every project I do. It would be very helpful for me for referring the details later when some bugs happen. Also, at the testing phase, this habit helps me a lot. Not only for project for all of my academic tasks including essays, irrespective whether it has been ordered from essay writing service(http://essayacademia.com), I maintain a short note for future reference.