Book work is a great app. Why I haven't bought it is because I haven't actually written anything requiring any level of organization, so I've mostly just tested it then trashed it.
Anyway, BookWork is great for one thing in particular, and is useful enough that I'll probably break dow and buy it if I start using it again: Writing RPG campaigns. NPCs go in characters, and the rest is all story. For THESE purposes I would like a couple more features, but beyond that, BookWorm is an excellent program. Maybe a "scrap paper" pad would be cool, just a place for unorganized random ideas to wait for the light of day... hmmm... email time.