Privacy is a major point of concern along with the fact that friends might use this service submitting photos of people who maybe don’t want this tech used on their likeness.
My biggest complaint is how long it takes for facial recognition to occur. I like searching by name, and if I do a large upload, I might have to wait a couple weeks to get the groupings. I don't get a push notification, I have to go check and suddenly I have 100 faces to tag.