A few days ago, I bought The Future of Reputation book from Daniel Solove. I had already downloaded it for free in PDF on my computer but bought it nonetheless for $9.99 on Amazon.com
The reason, according to Kevin Kelly most excellent article Better than Free: embodiment. Embodying the book in the form of a lightweight, low-power long-lasting reading device is something I value more than the content itself.
Kevin lists 8 other qualities that makes something better than its free counterpart, and although I list them below I encourage you to read the entire article: