In this brief and humorous presentation from TEDGlobal 2012, Paolo Cardini makes the serious case for monotasking. While not discounting the practice of "multi-tasking" - he does point out that really only about 2% of the population can do it (he doesn't offer a source for that stat).
Dr. John Medina agrees - there are just some things that you can't get done while multi-tasking.
Enjoy watching - feel free to comment and let me know your thoughts.