clipped from: news.yahoo.com 
NEW YORK - Researchers are studying a pervasive psychological phenomenon in which oh man we've got to finish doing the taxes this weekend ... C'mon, admit it. Your train of thought has derailed like that many times. It's just mind-wandering. We all do it, and surprisingly often, whether we're struggling to avoid it or not.
Michael Kane, a psychologist at the University of North Carolina at Greensboro, sampled the thoughts of students at eight random times a day for a week. He found that on average, they were not thinking about what they were doing 30 percent of the time.
For some students it was between 80 and 90 percent of the time. Out of the 126 participants, only one denied any mind-wandering at the sampled moments.