The German site, reported here, claimed that they had video and photo evidence of an improperly installed piece of heat sink foil. The theory went that this misplaced foil was causing the overheating.
Microsoft got on this quickly. The Gamerscore Blog ("...written by employees of Microsoft Games Global Marketing team.") has responded and claims that, "the thermal interface pads that are not installed incorrectly." Translated, that means the pads are installed correctly.
For the record, we haven't had any problems with our launch-day core system and we've had it turned on for many hours of many days. Of course, we give it lots of room to breathe.
What is interesting is that there are consoles that are overheating but nobody seems to know (or to admit they know) why.