This is the most recent survey we could find... we can only assume the numbers are growing.
"Workplace interruptions cost US economy $588 bn a year"
by The EditorsFinancial Express, 01/09/2006
Here is an excerpt:
Interruptions consume 2.1 hours a day or 28% of the workday and cost American economy $588 billion a year, a 2005 survey showed.
The survey by Basex, an information technology research firm, found that the time lost for productivity included not only unimportant interruptions and distractions but also recovery time associated with getting back on the task.
The survey reported in an issue of Time Magazine, was based on study of 1,000 office workers.
Estimating an average salary of $21 an hour for knowledge workers, those who perform tasks involving information, Basex calculated that workplace interruptions cost the US economy $588 billion a year.
A team led by Gloria Mark and Victor Gonzalez of the University of California at Irvine tracked 36 office workers and found that the employees devoted an average of just 11 minutes to a project before the ping of an e-mail, the ring of the phone or a knock on the cubicle pulled them in another direction.
Once they were interrupted, it took, on average, 25 minutes to return to the original task, if they managed to do so at all that day, Time reports. Workers in the study were juggling an average of 12 projects apiece, a situation one subject described as ‘constant, multitasking craziness.’
The five biggest causes of interruption in descending order, according to Gloria Mark of the University of California, were: a colleague stopping by, worker being called away from the desk (or leaving voluntarily), arrival of new e-mail, worker doing another task on the computer and a phone call