I just found a blog post about the selling of David Markson's library. Markson recently passed away and his collection of - often heavily notated - books was given to a bookstore to sell. As Alex Abramovich notes, this was a"shock, in part, because Markson’s work relied so heavily on other books". Needless to say, then, the notes he makes in those books provide potentially valuable insights into his own fiction. Now they're being sold rather randomly and scholarship may lose potential insights into his writer's mind altogether.
I discovered the blog post thanks to a Guardian blog by Sam Jordison. Once again, it goes to the topic of what happens now since you can't leave things in eBooks, but I liked the response of 'freepoland': "It is important to leave things in books [...] I leave bus tickets, cinema tickets, invitations, letters, ideas notes and all sorts; that way your book collection becomes a diary or set of random aide memoires. [...] I do draw the line at leaving a fried egg or bacon as bookmarks." I agree, egg and bacon may not be quite the things you should leave in books, although I think the odd pasta sauce stain can be found in some people's books. I'm not naming names.