I know Amazon isn't doing a whole helluva lot with the data they're collecting on me via their UI nor their devices; if they were, I would have a lot better recommendations than they offer to me on the regular. Yes, recommendation engines are hard, but Amazon has the computational power, resourcing, and data to do it well, yet they're simply not.
So. For now, I'm fairly convinced the data collected are useless/meaningless and I'm happy to go about my day w/o much worry. If I suddenly start seeing much better targeted recommendations, I'll rethink my strategy.