Insofar as the goal of an add is to make you buy the product that's being advertised, that the add be memorable, funny or emotionally evocative is not what makes it effective. That it makes you buy the product is.

Whether you remember the last Google add you saw, or even any at all, doesn't matter to them. That it makes people buy stuff is what matters and having effective adds is how Google makes money.

I remember a Superbowl commercial where cowboys where herding cats.

Did I ever buy anything from EDS? Nope. Do I even know who EDS was? Nope. Now that I do, do I have plans on building a company intranet on par with the U.S. Navy or MI5? Nope.

http://www.youtube.com/watch?v=Pk7yqlTMvp8

Does seeing an add for a highly related (well sometimes) product in gmail make me want to click on it? Sometimes it does. Does it equal a full-on conversion. Rarely. Very rarely. But as far as someone getting paid, just the click is doing that and it is very easy to measure a host of metrics revolving around it.

That TV ad might look pretty, but the ROI is far more speculative when you are basing them on emotion, aura, psychology, etc. rather than hard data which very well may be the math that definitively backs up the emotion and such.

Karmazin sees a girl selling beer. Google sees F 36-26-36 selling C2H5OH.