Multitasking appears to be less of a special talent and more of an ADD-type behavior: The frequent multitaskers in this study were just unable to focus on one thing at a time.
The people who multitask the most tend to be impulsive, sensation-seeking, overconfident of their multitasking abilities, and they tend to be less capable of multitasking.
From Who Multi-Tasks and Why? Multi-Tasking Ability, Perceived Multi-Tasking Ability, Impulsivity, and Sensation Seeking. Via The Atlantic. See also The Myth of Multitasking.