The excuse you've been looking for

According to research from the University of Melbourne:

Dr Brent Coker, from the Department of Management and Marketing, says that workers who engage in ‘Workplace Internet Leisure Browsing’ (WILB) are more productive than those who don’t. “People who do surf the Internet for fun at work - within a reasonable limit of less than 20% of their total time in the office - are more productive by about 9% than those who don’t,” he says.

Apparently because the short break increases workers' concentration subsequently.

UPDATE: The press release is dated April 2, 2009. One hopes the department didn't send it to their press office on April 1.