hahaha. when i read books, i tend to write in them. when they described images, what they remind me of, similiar stories that seem like the one i'm reading, predictions, key phrases, quotes i like, themes, questions i want answered. i fold the pages and crease the bindings. and on the back cover of the book (if there's no writing) i make a list of characters just so i can remember who they are.
i do all this with books i personally own. but i usually bother books from the libraury and i can make it through without turning down a page.