I have some news that should resolve the overheating issue that has been plauging a percentage of iPhone 3GS owners since its release.
I personally have not experienced this issue, however I have a very reliable source who claims that they have solved the issue thanks to some internal knowledge of a known issue during production. It apparently has do do with a corrupt software image when the 3.0 OS was flashed onto the devices during production.
The resolution is to reflash the iPhone via iTunes by doing a full restore with a downloaded image direct from Apple. The trick here is not to restore from your iPhones' backup in iTunes as that will only restore the corrupt image onto the phone again. To eliminate the problem you must have downloaded the full update from Apple, restored the iPhone to factory fresh with it and then manually reinstall all of your applications and data.
This is no doubt very time consuming, however I have been assured that this will solve the issue completely and is a known issue within Apple. I would be interested in hearing from any reader who has tried or has had sucess with solving the overheat issue with this process as I have not experienced it yet.