"Addiction is the continued repetition of a behavior despite adverse consequences, or a neurological impairment leading to such behaviors."
Would you say you have an addiction to Uber?
Would you say you have an addiction to Uber?
Social gaming (someone mentioned below) does, to a point, and then it's engineered to go way, way beyond that point.
It's complicated of course - and there's a spectrum - but I think a bad sign is if your architecture is intended to hack the reward systems of your customers.