Gary Namie, from the Workplace Bullying Institute (who knew such an institute existed) says "It's clearly a silent epidemic," and one in three of those affected by workplace bullying suffer from stress for more than one year.
How does bullying affect workplace productivity? It's estimated that 21+ million workers (40% of those affected by bullying) leave their jobs as a direct result of bullying. Because 72% of bullies are bosses, and most targets are non-supervisor workers, workplace bullies are not generally reprimanded.
Beach Bully image by Catnip Intoxicating [cc, 2.0]