56 Seconds
Average time an American spends looking at a Web page.
Source: Nielsen

"In another experiment, recently conducted at Stanford University's Communication Between Humans and Interactive Media Lab, a team of researchers gave various cognitive tests to 49 people who do a lot of media multitasking and 52 people who multitask much less frequently. The heavy multitaskers performed poorly on all the tests. They were more easily distracted, had less control over their attention, and were much less able to distinguish important information from trivia."

Some of us have been saying this  over and over and over.