There are other cases where the recommendation engine is not serving that function, because there is a lot of choice, and yet there's still no evidence that the recommendations are particularly good. There's no way to compare them to an alternative, so you don't know what might have been. If you want to put the work into it, you can play with that; you can try to erase your history, or have multiple personas on a site to compare them. That's the sort of thing I do, just to get a sense. I've also had a chance to work on the algorithms themselves, on the back side, and they're interesting, but they're vastly, vastly overrated.