How To (Ethically) Hack Amazon Categories

I get so many emails about Amazon categories and keywords that I thought it would be useful to dig into all the opportunities at your fingertips, and clear up some confusion out there too. Useful for me, that is. Now I'll have something to point people to! Should be useful for you too, even the old timers, because I bet there's a least one hack in here you didn't know about, and smart use of the category system can greatly increase your visibility on Amazon — critical for all authors, doubly...