Is the market even large enough? Have you thought about trying to up sell the entire book at the end of each summary? (Might get a few amazon.com clicks with e

Is the market even large enough? Have you thought about trying to up sell the entire book at the end of each summary? (Might get a few amazon.com clicks with each summary.) Do you know your churn rate and the lifetime value of each customer? I imagine it's too early, but once you have a good estimate you will know exactly what you can spend on adsense to drive more PPC traffic.