What I've always assumed, but now this thread has me doubting myself, but what I've assumed is that these systems, even though they appear to suck at specifically targeting me, must somehow be pretty good on the average, still netting big profits overall even though they don't seem to live up to the promise of getting me to buy stuff. But if everyone has this impression, maybe it doesn't work? I mean, I assume companies like Amazon and Facebook would be pretty good at least at optimizing the total rewards from using recommendation systems, but maybe you can't tell from your own anecdotal use. I have no idea. I'd love to see an analysis that includes aggregate numbers.