From an article in New Scientist magazine, April, 30 2005:

The next time your boss complains you are not focused enough, blame it on email and phone calls. Even smoking dope has less effect on your ability to concentrate on the task in hand.

At least that's what Glenn Wilson, a psychiatrist King's College London, found when he and his team asked 80 volunteers to carry out problem-solving tasks, first in a quiet environment and then while being bombarded with emails and phone calls.

Despite being told to ignore the interruptions, the average IQ of the volunteers dropped by about 10 points. Not everyone was equally affected - men were twice as distracted as women. Studies have also shown that IQs of people high on pot drop by only 5 points.

"If left unchecked, 'infomania' will damage a worker's performance by reducing their mental sharpness," says Wilson. "This is a very real and widespread phenomenon." Information overload can reduce a person's ability to focus as much as losing a night's sleep can, he adds.