I carry mine everywhere and jot down EVERYTHING in it: ideas, meeting notes, phone call notes, appointments, etc. I also use it to outline and draft articles, correspondence and any other writing I do.
As things get done or transferred to permanent platforms, I cross them off. As all items in one page get done, I draw a big X on a page. When both sides of a page have Xs, I tear the page out.
I don’t keep my notebook. I have no sentimental attachment to it. It helps me keep all notes in one place and get things done. When all notes have been filed and all tasks completed, I throw away the notebook and start a new one.
Inspiration for this post comes from Design Observer.