Right now, somewhere in this world, someone is masturbating. As you read this, someone else just increasedtheir device to vibrate a little faster.
I don't think anyone can argue that I've violated anyone's privacy by stating that. That's the equivalent of what this discovery, as written, entails.
Maybe I'm not as overly-conservative (bordering on prudish, if I may say so) as you. If I bought a toilet or seat that monitored how often [the user] took a dump, really I don't care. Frankly, in that particular instance, I wouldn't even care if they knew it was my account/username that was taking said dump. Pooping is not a shameful act. So maybe that wasn't the best analogy on your part.
I would argue that study groups are MORE personally-identifiable and intrusive than this method of data collection. Sure, people are 'signing up' for it, but you know who the testers are, and they know they're being tested - possible data skew.
I'm not saying that the company shouldn't adjust how they do this (others brought up proper disclaimers, and I think an opt-out button would be good), but again, I find it extremely difficult to justify the word "caught" in this instance. If no PII is sent, I truly do not see the issue. Sex is not embarrassing.