"In one study, a
site provided links to related books on Amazon.com, which opened in a second
browser window. Using Amazon wasn't relevant to our test, so as soon as the
page came up the users tried to back out. One pair of users, upon
discovering the grayed-out "Back" button, looked at each other with
something akin to horror. They were quite honestly stumped and had no idea
how to proceed. After a couple minutes of discussion, they finally closed
the second window. In another recent study, six out of 17 users had
difficulty with multiple windows, and three of them required assistance to
get back to the first window and continue the task."