Pop-up ads are, in a word, annoying. But surely they must work. Otherwise, the Web wouldn’t be overrun with them, right?

It ain’t necessarily so, says a paper from the Wharton School of Business. In this part-research, part-opinion piece, several experts at Wharton and elsewhere challenge the effectiveness of pop-up ads. They even question whether the day is coming when advertisers will forsake pop-up advertising. Granted, pop-ups are cheap, the experts say. But advertisers have to wonder whether it’s wise to use a medium so irritating that the audience actually pays good money for software to keep the ads from detonating.

Why are pop-ups so reviled? In part, it’s a function of the medium. When people are online, they don’t like to be interrupted. Pop-ups are a bigger imposition for users who connect via slower connections – nothing is more aggravating than waiting what seems like an eternity, only to load a Flash-powered online casino ad.

But all is not lost. Advertisers can learn to use pop-ups effectively if they think about how to be less intrusive and more helpful. For instance, people merely surfing the Web are less likely to mind pop-ups than those who are searching for information. And every Internet visitor has some information he’s happy to receive via pop-ups. Good advertisers, the Wharton experts say, will try to find out what the individual user wants and deliver it at an appropriate time.

“In the final analysis,” the article states, “all advertising is an imprecise science. No one knows with any degree of consistency how well any ads increase the sales of products and services. Sometimes they help; sometimes they don’t. The better ones can create a nice positive buzz; the poorer ones can be embarrassing.”