There has been a lot of studies recently that indicate that multitasking is harmful to productivity. In other words, there are significant switching costs when you mentally move from one topic to another. There is a New Atlantis article summarizing the findings entitled The Myth of Multitasking. Ironically, this story was picked up by Slashdot, one of the larger disrupters of concentration in IT. My high school algebra teacher knew all this a long time ago as he would always tell us, "age quod agis": do what you are doing.