As a voracious reader, I've personally found that I got the most out of books when I stopped trying to summarize and highlight. I very rarely do either anymore.
I realize that what happens is sort of a Darwinian "survival of the fittest ideas" in my head, often subconsciously. Once I relaxed and decided, "If the stuff in this book is good enough, my brain will keep it FOR me" both my satisfaction AND utility of books increased dramatically.
(which is to say, it's not that I never write anything down. It's that if I do, it's not tied to the book, but to the "thing" or "topic" that I'm interested in, with a reference TO the book)