I've found that, besides 'to do lists', the other stuff that I do with notebooks – ie. write down various types of notes – has become an unmanageable mess. (Or at least, a mess that needs to be managed to be effective, and I don't want to be spending time and effort "managing" notes.) So I'm taking a long, hard look at exactly what I want to write notes for – where I'm duplicating efforts, and where there might be some gaps that could be filled.