I purchased a used copy from Better World Books.
The Art of the Handwritten Note is sort of a love-letter to the practice of sending brief messages in your own handwriting. It encourages picking up a pen instead of shooting out an email whenever possible, and it gives tips for those unsure where or how to start.
The author is a professional calligrapher and apparently an opinionated one. She is pretty adamant about which kinds of paper and pens one should purchase, and she lays out a lot of rules about practically every note-writing situation. In some cases these are helpful, in some cases they are just common-sense, and in still others giving her personal preferences the weight of law is simply silly.
Helpful for those who struggle to say the "right thing" in a sympathy card or those who never received training in writing a proper thank-you note. There are a couple of good examples here and there for various occasions. Otherwise there is little of substance that is not adequately covered by Emily Post.