Rumors of a new DS make this kind of news a little juicier: Nintendo at the end of last month filed an addendum to a 2005 patent that describes a vibration feedback system, this time coming through the stylus.
There's a lot of "vibrating said vibrator in a vibration pattern"-type speak in the filing, spotted by Broke My Controller (you may read the full document here.) But the crux of the matter is that players would press the stylus into the DS' touch screen, attacking an enemy character, for example, and then feedback would come from the device itself, being felt through the stylus. The amount of feedback is calibrated to in-game events - strong or more successful attacks produce more, weak or unsuccessful ones produce less.
Of course this wouldn't make the first time Nintendo has looked to add vibration functionality through its handheld. There was the Rumble Pak expansion of 2005, which was poorly received and supported by about 40 or so games. It's also incompatible with the DSi.
Nintendo Patent Reveals What May be Tactile Feedback Felt Through DS Stylus [Broke My Controller]