Joystiq has a piece up with a quote from a former GameStop employee commenting on just that. I dunno how the QA/QC guys even let units out the door with a flaw like that if what they're saying is true...

"Apparently, 300 PS3 Units were created and sent to various software developers to begin creating games for the new system. However, design flaws in the PS3 (Specifically, not enough coolant) caused the systems to overheat and meltdown after moderate use by the developers."