It seems that every month new reports of computers going up in smoke surface. A video has been posted online from a Chinese reporter who was using his iMac when smoke started pouring out the back of his machine.
The computer appears to have adequate airflow around its vents and doesn't appear to be placed in an area where temperatures would exceed normal operating conditions. Hopefully this iMac will be shipped back to Apple so that they have a chance to examine what caused the smoke and will be able to take precautionary steps to avoid this again in the future.
Apple is not the only one who has had problems with computers bursting into flames. All of the major manufactures have had some issues but each incident is isolated and has yet to become a wide spread problem.
The only way for the vendors to know the true cause behind situations like these is if the consumer contacts the manufacturer immediately. By alerting the appropriate vendors they may be able to determine the cause and avert further issues in the future.