The OmniFocus Video Field Guide is a screencast, not a book. A lot of people have asked me to write a book about OmniFocus but instead I made this 2.5 hour video that takes you, soup to nuts, through the Omni Group's supremely bad-ass task manager. The screencast can turn an absolute OmniFocus novice into a task-managing ninja. - David Sparks
Buy two copies. Keep one for yourself.
Put the other one on an USB stick and gift wrap it together with David Allen's Getting Things Done. Gift it to an overworked friend or family member. They won't understand the present at first, but they'll thank you for it in the future.