Great story! But am I understanding this correctly that all the author did was approaching a few blogs with promo codes? And after a few days with relative low traction pretty much gave up on promoting it, just setting it on free? Not even slapping a few ads on it?

Is there some general "formula" on how much ad revenue one can expect from a (relatively straight forward) free app per 1000 users? Meaning some help on at what point would it make sense to move from sales based monetization to an ad based monetization model.