We ran it paid as a test in Jan 2011 when we started YC. Apple featured it at $1 and we made something crazy like $10000 in a couple of days. The intention was

We ran it paid as a test in Jan 2011 when we started YC. Apple featured it at $1 and we made something crazy like $10000 in a couple of days. The intention was to have a subscription service as we expanded into a more FitnessKeeper-like space. However, our users were generally not receptive to that and used it in too much of a casual way to up sell. Plus, we started to realise by this point that the opportunity was a lot smaller than we'd thought. We tried IAPs for a bit but that failed miserably for the above reasons. Ads too for the same reason.