Send: The Essential Guide to Email for Home and Office by D. Shipley & W. Schwalbe

Very interesting, indeed. The book discusses the ways in which email is similar to other correspondence, how it is different, and what the pitfalls of email can be. It also discusses email etiquette (when to CC someone, when to BCC them, what kids of things are appropriate to send via email). It's written in a down-to-earth, easily accessible style. I enjoyed it and I learned a lot.