I'd been thinking about "design for engagement" after iBooks unilaterally decided that I would want to set a goal to read for 15 minutes every day. There was no way in-app to disable the behavior, only to change the duration. I did eventually find a toggle to disable it way off the bottom of the screen in the Settings app, but still, how hostile is that? I just wanted to read something, not sign up to define my entire personality by my iBooks usage.