The Atlantic Monthly recently ran an article called "The Autumn of the Multitaskers", by Walter Kern (subscription may be required to read the article). He talks about his own conversion from multi-tasking to single-tasking as his car flew through the air towards a telegraph pole as a result of trying to look at a picture sent by his girl friend to his cell phone while driving. He lived to tell the tale, but only tells that tale when he is not doing anything else.
Kern quotes Publilius Syrus, a first century B.C.E. Roman slave: "To do two things at once is to do neither." This old wisdom seems to stand up to modern research. Kern notes that neurologists are finding multi-tasking is bad for the tasks you are doing all at once, and actually bad for your brain, too.
I for one plan to stop multi-tasking, or at least I plan to stop multi-tasking when I am doing something else, anyway.