I grew up with the idea that you never, ever write in a book. Unless you're correcting a mistake. (The book never "gets it" except when the book deserves it.)
But I was wrong. Tim Sanders fixed me. His book, Love Is the Killer App: How to Win Business and Influence Friends, in the section about Knowledge (page 82) just saved me a few hours. Tim recommended to me that as I read, I should tag and cliff within the book itself. His advice made me uncomfortable, because it made good sense, but I do not write in books.
So, I was just wrong. I didn't summon the courage to tag or cliff Tim's book, but I resolved to tag and cliff the next few. And wow, it's a Good Thing. It's basically the act of creating an index for stuff you want to find later. I just saved myself a couple of hours looking for a passage in a book that I found in about 30 seconds because I had tagged it inside the front cover. My tag told me the page number and the concept I was looking for, and—poof!—I snapped right to it, there it was. That's index access by rowid for the brain.
Now I write in all the books I read. It works, and I highly recommend it.
Thank you, Karen Morton, for giving me the copy of Tim's book.