Last year, I visited the office of a newspaper editor who I write for on occasion. I was there to talk business, but as I glanced around at all the books on the shelves in his office, we couldn't help but get off track a little. He and I hold relatively similar worldviews, so he felt free to suggest a number of books to me. While I browsed through his copies of the books he suggested, I noticed that he underlined passages and made quite a few notes.
I haven't always marked up my own books, but in recent years I've made notes in every book I've read—even fiction, because it helps me to find passages at a later date and somehow just underlining passages seems to lock information into my mind better. I've event started jotting down notes when I watch DVDs. Movies contain so many good quotes that it seems like a shame to me to let them go unrecorded.
When I asked the editor about the markings in his books he said that he has a "working library." I like that because it implies that his books aren't just decorations, but instead, they become part of who he is. And that's exactly why I started recording quotes, underlining sections of books, and making notes several years ago. I don't think the arts are meant to be consumed only once. Instead, they are to be explored, and pondered, and savored.
And it's in the savoring that they enrich our lives.