Maybe I'm reading this wrong...

But leaving a drop-down ad on too long could be counterproductive.

The new research, led by cognitive scientist Mark Changizi of Rensselaer Polytechnic Institute, shows why direct exposure to repeated ads initially increases a consumer’s preference for promoted products, and why the most effective advertisements are the ones consumers don’t even realize they have seen.
It has long been known that repeated visual exposure to an object can affect an observer’s preference for it, initially rapidly increasing preference, and then eventually lowering preference again. This can give way to short-lived fads. But while this may seem illogical, Changizi argues that it makes perfect cognitive sense.
“A rational animal ought to prefer something in proportion to the probable payoff of acting to obtain it,” said Changizi, assistant professor of cognitive science at Rensselaer and lead author of the study, which appears in the online version of the journal Perception. “The frequency at which one is visually exposed to an object can provide evidence about this expected payoff, and our brains have evolved mechanisms that exploit this information, rationally modulating our preferences.”
A small number of visual exposures to an object typically raises the probability of acquiring the object, which enhances preference, according to Changizi.
On the other hand, Changizi says overexposure to an object provides the brain with evidence that the object is overabundant, and is likely not valuable, thereby lowering the individual’s preference for it. [More]

As newspapers die from advertising starvation (and customer disappearance - car dealers can account for as much as 40% of newspaper ad revenue) much of the blame is placed on ad dollars flowing to the Internet.  But so far, monetizing on-line traffic has not proven easy or as lucrative.

And there have been some discoveries of what not to do.

One reason may be captured above.  Ads need to be ubiquitous, but only to a point.

Not that I'm hinting or anything...