Much probably multitasking is impossible if you think (as you are all thinking) on "time" in discrete mode. But time is continuous. In discrete mode, it's really easy to think about compartments of reality ("reality slices"), and via this way, to wrongly embrace and compart every context and concept in separate modes (which is, if you allow me, another vision of what's really going on); one for the work anyone is doing, another one for the sound or TV or whatever, buzzing around us.
I think this discussion is cursed ab-initio; that is, cursed by the word-definition in itself. The word comes from a computer-based computer-science realm. Where (at least now) time is still discrete. CPU's even fast as they are nowadays, still handle each single task at each time. If not (in parallel mode - a via for multitasking -, following any of the possible protocol paradigms available today, some of which self-organized), they thread it to another neighbour friendly CPU, which again only treats the next task after completing the present one.
However, much tiny slices (so tiny that their division becomes indifferent) are indeed the answer for real-world continuous time-space discernation and decision. As you may be aware, we are now speaking of animals, not computers. And if they indeed become so tiny, they end up being real-time connected thougths (who really knows which neuron is firing rigth now - and who knows if the TV is ON, what happens to that precise neuron in the same circumstances - a mammal doing some serius work - It would indeed fire again or not? Or the neuronal path will be entirely different, being the final result exactly the same? Or not?). Reality in fact is non-linear. I am sorry if it sounds romantic - which I hate it.
There is more to life than mechanics - there is also dynamics. Life depends critically on principles of dynamical self-organization that have remained largely untouched by traditional analytic methods. There is a simple explanation for this - these self-organized dynamics are fundamentally non-linear
phenomena, and non-linear phenomena in general depend critically on the interactions between parts: they necessarily disappear when parts are treated in isolation from one another, which is the basis for any analytic method. Rather, non-linear phenomena are most appropriately treated by a synthetic approach, where synthesis means "the combining of separate elements or substances to form a coherent whole". In non-linear systems, the parts must be treated in each other’s presence, rather than independently from one another, because they behave very differently in each other’s presence than we would expect from a study of the parts in isolation.
Rather, every part is a behaviour itself, and life is the behaviour that emerges from out of all of the local interactions among individual behaviours.
So then, what happens to different inputs coming to same source at the same time, and treated non-linearly? As our redundant millions of neurons do?
For all of this reasons, I think the article "The Myth of Multi-Tasking" was done by a computer (aka Merlin Mann). Fast-food for thougth. The title indeed, is quite disturbing and intriguing (if not ridiculous); ... "in 43 folders". No doubt this sequencial material comes from a compartmented computerized mind. Why not 44? Could he not multitask logically another folder?!
And much more. Following this article, which is pretty much like a receipt, we could even think - and dare! - of forecasting human behaviour. From this 43 "rules" it seems quite straightforward to achieve that goal. However, let me ask you, could you seem possible to predict human behaviour?
Humans in fact are opening simultaneous related "folders" for years, as any conversation goes on (emergent behaviour). That's why we in generally search for quiteful places for reading a book. We even reason on that eventual decision based on the quality of the book. In order for not having him - as much as possible - altered. Thoughts are sporiferoleuous connected to the environment, and they move on, not in discrete time. If you really could compartment them, well..., let me congratulate you for having reach the pure ZEN state. Indeed, we Humans, we are multitasking everything since we were crawling in caverns. Our relation with artifacts are a good example.
On the other hand, for this Merlin Mann, eventually, that's our problem. We are crawling from the very first artifacts to these frigid folders!