It boggles my mind when HN commenters start claiming that measuring ad campaigns is impossible or that ads are universally ineffective. Anyone who has spent time working with large ad campaigns should know the tools and methods used to measure these things.
I suspect the HN sentiment comes from a common feeling among techies that they are somehow immune to influence from advertising, combined with a high adoption rate of ad blockers. HN commenters tend to assume that other consumers are just like themselves, which is far from the truth. In the real world, advertising (when done right) is not only very effective but not that difficult to measure using modern technology.