"There is also consent by action. The casino does A/B testing by offering some a $40 steak dinner plus $40 in chips while it offers others $80 in chips. You clicked on the advertisement/offer, or you opened the envelope that arrived in your postal mail, etc."
Well I think this is the difference, when you sign up to OKCupid you're signing up to a service that's explicitly designed to optimise your chance of meeting someone, so almost by definition you're going to expect them to play around with your profile, their matching algorithm and so forth to optimise that goal.
I'm pretty sure however that no one signing up to Facebook did so with the belief that Facebook would try and play with their emotions to make them unhappy.