Companies that allow employees to sign into Facebook on the clock are losing 1.5 percent of total employee productivity.So says a survey by Nucleus Research Inc., which interviewed 237 randomly selected office workers about their Facebook use. Admittedly, that’s not the most scientific sample, but it does give a snapshot.Of those interviewed:• Seventy-seven percent had a Facebook account. • Of those with Facebook accounts, nearly two-thirds accessed Facebook during working hours. • Those who