Harmless office chitchat - or poisonous gossip?

An office where people spend a lot of time undermining each other's reputations is not a healthy place, writes Fortune's Anne Fisher in her November 5 Ask Annie column. Do you think the office grapevine is beneficial, or is gossip a big problem in your workplace? Have co-workers ever made you the subject of unfair rumors? Any ideas on how to keep the rumor mill from running amok?