This is anecdotal evidence. Nobody is disputing those exists. However I think FB and Google owe their existence a little better evidence, such as A/B testing, control group studies and even experiments to actually demonstrate their effectiveness. Until we have those (and perhaps we do; I seriously know nothing of the existing literature) the anecdotal evidence we do have should be taken only as indicative of effect, not proof of effect. Anecdotal evidence come with a ton of bias.