Discover Magazine references several studies on the importance of zoning out, including a University of Santa Barbara case that asked participating students to read from—what else—War and Peace and to tap on a computer key when they weren't thinking about the book. On average, the students reported wandering off topic 5.4 times in 45 minutes. Depending on the experiment, we may spend even more time—up to 50 percent to be exact—not thinking about the task-at-hand.

All of which, the article says, is a good thing.