Anyone who's given a PowerBook, MacBook, or MacBook Pro a good look probably knows how the ventilation system works: two inlets near the front of the computer draw the air in, a big vent grid underneath the screen hinge lets it all out. Ideally. Except Gert Stahl apparently discovered a thin layer of plastic film in his MacBook that prevented airflow, and was causing his machine to overheat; removal promptly caused his fans to shut off and the machine's heat to return to a level more manageable. What's more, apparently there was never any mention made in the manual about the removal of any such film, leading one to believe that this might be unintentional (read: manufacturing error). So, if you've got a MacBook and it's a little toasty, check that gap out for the thin plastic strip -- if you've got the film (or if you don't) then you let us know!
Update: Well, it looks like the court of public opinion has ruled on this one... doesn't appear to be the real deal. If you've got a blocked vent, well, you obviously didn't speak up. So for now we're gonna close this case and move on with our damn selves.