Perfectionism - healthy and unhealthy

Everyone who works in marketing has met him - or her - the obsessive, tyrannical perfectionist who picks apart every idea, tells everyone they're rubbish and then burns the midnight oil reworking other people's efforts until they no longer resemble their original author's intents. But perfectionism isn't necessarily destructive and disempowering - it's a driving force for success and for some of the most memorable and influential creative and strategic campaigns. What does healthy perfectionism look like, and where's the dividing line beyond which things get painful and counter-productive?