Google Adsense Policies clearly states that "Clicks on Google ads must not result in a new browser window being launched." Adsense publishers are neither allowed to alter the HTML code nor can they give their visitors an option to open Google ads in a new browser window. But according to a report published in The New York Times, a majority of web users are responding to banner ads indirectly - they avoid clicking the actual banner advertisement on the website but type the advertiser's URL directly in their browser.
About a third of consumers sometimes click on banner advertisements on the Web. But twice as many consumers sometimes respond to such ads indirectly, avoiding clicking on them but later visiting the Web sites advertised.The main reason for this behavior is that consumers want to continue staying on the website where they first saw the ad. Clicking the ad unit would mean navigating off the current webpage.
While this behavior will not affect the performance of CPM (or impression based) ads, publishers with CPC ad inventory are getting hit definitely.
"People are engaged in the content they’re looking at the time that they’re exposed to the ad, and they don’t want to navigate off the page," said Rick Bruner, DoubleClick’s director of research.
Maybe Google can give a small check box in their large ad units that would allow users to decide if they like to see the advertiser's website on a new page or the current window itself. Incase of Flash banners, such an option could be added to the context menu of the flash player easily.
Probably, everyone would benefit from this.
Read: Click on Me Now or Visit Me Later
Adsense Feedback - Open Links in New Window (seen on Youtube)