Look up "retargeting". Creepily chasing people around the web is successful for advertisers.
My mom (again) is subjected to retargeting, but she doesn't identify it as tied to her identity so much as tied to the current search. She uses gmail for work and her personal account (because i set up a google apps account for her), but I doubt she knows that just because she's logged into gmail that google search is tying that information back to her identity.
This is a far cry from Facebook where people know that things in Facebook are tied back to their identity, and not only that is tied back to their identity in a way that may be visible to friends and family.
Both Google and Facebook track you, but Facebook is personal, and people are aware of that fact.
Yes, it's annoying if you're in the 95% of customers who won't actually convert. But it only has to be effective about 1 out of 20 times to be a huge improvement (and that 1 might even be you, but you're mostly annoyed by the other 19 times.)