It turns out multitaskers are terrible at every aspect of multitasking. They're terrible at ignoring irrelevant information; they're terrible at keeping information in their head nicely and neatly organized; and they're terrible at switching from one task to another.
Multitasking is one of the most dominant trends in the use of media, so we could be essentially dumbing down the world.
(Source: PBS.org | Interview Clifford Nass)
A long, but fascinating article discussing the effectiveness of multi-tasking.
Turns out, according to the research, it's not.