Everywhere I have read, says that burning slower can avoid problems, and burning over the rated speed (ie burning a 4x at 16x) makes the problems. Atleast on older drives this was true, due to the material used in the disks, since the laser has to "burn" the information on. Running at too fast of speed, would leave the laser too short of time to "burn" the mark on the dvd/cd. Running at lower speeds, can have the laser either run at less power, or so i'm told, never had the will to take a screwdriver and see what makes them tick :)

But I never have a problem, and have burned almost 200 DVDs in the past 6 months, not one coaster, drive is 16x and I usually burn at 8x or 4x, so without seeing his computer first hand, all i can say is what is different from what I do.