Again, on the topic of pop-under ads

InteractiveWeek discusses the Jupiter Media Metrix report in 'Pop-Under' Ads Mostly Ignored. Web advertisements that launch in a new browser window - have become more common, a new study suggests that they may be an ineffective form of advertising. However, while Jupiter Media Metrix continues to include traffic from pop-up and pop-under ads in its overall traffic statistics, the firm cautions that it is "impossible to determine" whether a user intended to visit a site or whether the visit was the result of a pop-up or pop-under advertisement. ... Jupiter Media Metrix estimated that between January and May 2001, reached 32.8 percent of the Web's entire audience with its pop-under ads - in other words, about one-third of all surfers during that period were served an X10 ad. However, the study said, 73 percent of those who were served an X10 ad left its site or closed the pop-under window within 20 seconds.