The Consumerist has the tale of a PS3 owner who claims that Sony told him the dust on his console voided his warranty. Sony, however, saw it a bit differently. They claim that the PS3 in question wasn't just dusty, it was positively filthy:
"The examination of the unit in question that SCEA's service center conducted upon receiving it from the consumer revealed that it was the subject of extreme consumer abuse or neglect not covered by the PS3 warranty."
Sony took pictures of the PS3 to prove their point...
(Please note: the picture accompanying this post is not a picture of the PS3 in question. It's just another dusty PS3.)