All things being equal (money, space, etc), would you rather own copies of the books you read? Or borrow them?
I would definitely buy them. I have a book buying addiction. I love just looking at them all lined up on a shelf. Surounded by a nice reading chair, a soft glow lamp, a cup of tea, and a comfy pillow, I would reveal in the beauty of the books. Rarely, I would give away a very special book to a friend, but most would stay pretty on my shelf until I reread them.
Alas, I have neither money or space to buy books. I borrow, and borrow, and borrow some more.