In a recent usability test I observed, about half the participants actually got lost. With the new window completely covering the original site, they did not notice that they had two (or more) windows open. In an attempt to return to the original site, they repeatedly hit the back button. When that didn’t work, they totally closed all browser windows and completely started over. Despite the fact that some sites insist on opening new windows “so the visitor doesn’t lose our site” when in actuality, the new windows appear to actually cause people to lose the site rather than keep them.
The scourge of new windows – why you should not force website visitors to open links in new windows.