Unexplained malfunctions, battery failure among common complaints This holiday season Apple Computer Inc.'s iPod is once again a top seller in stores, and the music player's white earphones remain a nearly ubiquitous sight on city streets and at gyms. But as it reaches deeper into the mainstream, more users are becoming familiar with a new sense of loss: the death of an iPod. Among users of the device, it's long been common to hear of iPods laid low by batteries that no longer hold a charge, malfunctioning hard disks and screens with cracks. In some cases, problems are caused by...