Handwritten notes (even if not reviewed) provide a physical (touch of the paper, movement of the hand) sense to the auditory/visual experience of the lecture. Paper books bring, again, a physical (smell, touch, movement) sense to the act of reading. I've held the same iPad for dozens of books. But I've only held one copy of TaoCP or A Wizard of Earthsea. The hardback covers, the library card, the feel of the worn pages, the smell of the paper, all come together in the mind to create a stronger memory when recalled. This, in turn, is tied to the memory of the contents themselves and so I can recall them with greater ease than from an ebook. Of course an ebook or typed notes offer more than just an audio book (though the experience of a particular road trip tied to the listening will help as much as with the print book) or a lecture with no note taking.