In my seventeen years online I’ve never ever bought a product or service based on an ad. I’ve bought from newsletters but never from ads. The difference the way I see it is that newsletters are highly targeted because they originate from a web site that I <i>frequently</i> visit. Whilst ads rarely take into account the frequency of your searches. You happen to search for shoes once and then for weeks, or even months, after you’re bombarded with relevant ads.