When I read, I'm constantly analyzing and trying to learn from my betters. Armed with a pen, a highlighter and post-it notes, pages are unceremoniously folded and comments are often scribbled in the margins (about the story's arc, the narrative drive, character development). I slap post-it notes on pages I admire, noting a great piece of dialogue, a scene that moved me, a well-crafted subplot, the author's ability to set a certain tone or foreshadow, etc.
When I'm done, the pages are often dirty and the book looks like it's been through a bad storm. Some people would cringe if they saw my collection of books, but to me they looked 'loved to death' which is a compliment to the authors who wrote them, wouldn't you agree?