GREAT ARTICLE! I must say, I've experienced the same results with Facebook ads. Useless! Facebook users comment and 'thumbs up' ads, but they DO NOT buy or sign up. I've noticed many FB users will negatively comment on ads or start conversations on the ad's comments that have nothing to do with the ad itself. Waste of money.
I tend to think that it has to do with the intention that people have when using Facebook. It's more of a procrastination platform than a tool for any particular purpose, an so even if we see something valuable on Facebook, the timing and mood is not conductive to anything by browsing the feed and clicking "like".