A recent study claims that dust on computers and other electronics contain a chemical residue that can possibly pose a long-term health threat.
From CNET, "In a report published by Clean Production Action and the Computer TakeBack Campaign, two groups studying environmental and health issues related to computers, researchers contend that potentially dangerous elements of brominated fire retardants are turning up in dust samples swiped from computers. The research indicates that the most commonly found example of these substances, widely used fire prevention compounds known as polybrominated diphenyl ethers, or PBDEs, have been found to cause health problems in lab animals."