Out of the corner of your eye
There's no such thing as coincidence.
Of course, the human mind, in its neverending quest to create meaning, invents coincidences all the time.
I'm a big fan of modern art, but I admit that I had never heard of April Gornick.
Tom Cohen, a board member at Squidoo, knows April.
Today, I did a search for a gas station near my house that would put snow tires on my wife's car. Typed in my town and the word GAS into google.
Guess what the seventh match was?
The art of April Gornick.
Of course, I never would have noticed this if Tom and I hadn't been discussing April the week before. My point, and I do have one, is that search makes it far more likely that you notice something that you weren't expecting. Bookstores are great at situational selling, at exploiting the proximity effect to help you discover something you didn't think you were looking for. Amazon isn't nearly as good at that (though they're trying.)
I think it's inevitable that Google will start featuring thumbnail photos in adwords--it will dramatically increase the chance that a surfer's subconscious will pick out a tiny detail that leads to a click.