I've been Co-Lead iOS Developer at Farfaria, the so-called Netflix of kids' books for over a year now. Some of the fun things I've done are...

> Built a social layer called Book Club, that lets you share your Favorite books with friends. It has lots of nice Facebook SDK hooks.
> Designed and built many successful A/B copy and UX tests within the app, using Mixpanel's A/B Test platform. The most successful was a post-read subscription promo popup (after a free user's single free book per day), which led to a 16% jump in subscription purchases.
> Built a view-independent popup class, with blocks-based callbacks. It handles a multitude of content views and works swimmingly on all iOS devices, in all orientations.
> Built an Analytics Log, that shows events info, on device, in real-time. Great for QA, if I do say so myself.
> Upgraded project to Cocoa Pods, and ported all 3rd party libraries.
> Re-engineered Book Shelf view to be an infinitely scrolling collection view, instead of a page view.