For the record, I tend to only use it myself when it really adds something big to the game. Examples - Ocarina of Time used it to indicate/guide the player to secrets with the rumble stone, Waverace Blue Storm because it adds no end to the feel of racing on water. But for the most part it tends to add nothing to games - I`d find it hard to say the controller shaking has any purpose whatsoever in a beat-em-up or such. Just figured it`d be interesting to find out what people make of it.
The best use of rumble was probably in Metal Gear Solid on PSOne, when Ninja tells you to put your pad on the floor and tells you he's gonna move it. There wasn't one person that didn't shit themselves.