This doesn't really bother me. As noted, the T&Cs specifically say your data may be used in research. I'm also not entirely sure how they're supposed to improve

This doesn't really bother me. As noted, the T&Cs specifically say your data may be used in research. I'm also not entirely sure how they're supposed to improve recommendation algorithms — which we're all clamoring for them to do — without running some form of experiments with them. The question to answer is, did they do it as ethically as they could? Just based on this article, I don't see any unpardonable sins.