We're really not sure if Sony was being serious when they said they'd be willing to replace the lithium-ion batteries in the PlayStation 3's Sixaxis controller if and when they stop holding their charge, but their "Safety and Support" manual (included in the retail box) seems to indicate otherwise. On pages 18 and 19, they detail how to remove the battery before disposing of the controller. Sure, they're not telling you it's cool to replace it yourself but follow those steps in reverse with a new battery, and you've got yourself a revitalized Sixaxis.
What they are telling you how to remove and replace is the console's hard disk. Follow a handful of instructions and you can replace that anemic 60GB drive with a whopping 200GB monster ... all without voiding that warranty!