If you think about the traditional view that the book is only about the text, then this is kind of foolish, I suppose.

Paul Ruxin, Caxton Club, on marginalia: via NYT

Studs Terkel would admonish friends who would read his books but leave them free of markings. The phrase mark my words, after all, describes as much one’s attention to the words as a tactile interplay between the text and the engaged reader who, having become so taken with the spirit of the writing, draws up a pen to affirm, debate or deny the letters on the page. Over time, the presence of marginalia, marking, and other indications of the reader has varied in its reception, from the most open and appreciated to the closed and displeased view of a caricatured librarian or the utter refusal to countenance as much by contemporary ebook reading devices.