We could categorize ads into value-added, passive ads versus brute-force, active ads. Passive ads don't only push a product, but provide some useful content for

We could categorize ads into value-added, passive ads versus brute-force, active ads. Passive ads don't only push a product, but provide some useful content for the user, be it music discovery or news aggregation (I guess calling it intellectual stimulation would be reaching, though). The purpose of active ads is to simply push a product and entice the user to buy now. As such, they vie for attention and usually interrupt the user's workflow. Examples of passive ads: music discovery [pandora], news aggregation [HN], etc versus active ads: traditional ads (TV/radio/internet/magazine) and active product-pushing. As an aside, I am aware that Pandora has ads which is kind of mind boggling - they are actually providing free advertising to the music companies by letting me discover new music, yet they still have to pay royalties, so they are forced to use ads.