It is funny, how people trying to make old stuff new again and again. =)
The power of concentration, focus, impulse refusal and self-control were praised even in Upanishads. Then the Buddha become a great teacher to everyone, next this teachings was evolved into Zen and so on.
Most resent psychiatrist rediscover it again and again as 'gestalt therapy', 'curing experience', 're-framing' and other 'great findings'.
Read something on today's hot topic 'social intelligence' and you will find re-selling exactly the same ideas (from Hindu/Buddhism teachings) along with co-called 'scientific evidence' like scans of brain's activity and the like.
I didn't even mention the Matrix movie =)
In the essence, multitasking is about to decrease your productivity, because this misconception is based on concept that came from an IT field.
In IT multitasking emerged because you have too many unused CPU circles and they could be used to do some additional, background processes. Even today and average server spend most of its time in the idle loops.
In a dramatic contrast, our mind have no idle loops or unused powers. Often people have some deficits instead, like lack of focus, inability to concentrate long enough, to pay attention and so on.
Of course, it is acceptable to listen your ipod while you're doing some hard, dumb, physical job, that distracts your attention from the quite boring task. But if you're trying to use your mental capacity any distractions reducing your efficiency.
Some people are confusing multitasking with creativity, which is an ability to associate and link together things from quite different fields (say, Buddhism and modern cognitive therapy =)
So, it's much better to try to learn some thousands-year-old techniques to boost your concentration, focus, attention and some relaxation and priming up methods, instead of reading crappy blog posts. =)