Agreed. Even worse people who do it to library books..... it's not your book so don't treat it like it's yours to do with as you like.
Im reading through a book now with a tremendous amount of scribbles and underlines in it. I want to read the book, not your thoughts on the authors theories or what you find important, that stuff is mean't to go in your notebook

(I find my ereader much more comfortable, especially as when I'm reading a paper book I tend to take great lengths to protect it from undue damage).

