The newest PlayStation 3 system software update to version 1.94 adds firmware-level support for the upcoming rumble-enabled DualShock3 controller. Though the update is not yet available for download, it's bundled with Insomniac's Ratchet and Clank Future: Tools of Destruction, the first retail game with built-in support for the DualShock3.
By pressing the middle PS button on a PS3 controller, the DualShock3's rumble can be toggled on or off from the Controller Setting menu in-game. Listed as the "vibration function," rumble will obviously only be felt with DualShock3 controllers and not the rumble-less Sixaxis.
Sony plans to release the DualShock3 in Japan this November, with the peripheral coming to the U.S. and Europe this spring. Until then, check out the Shack's list of game's that will feature or be updated to feature DualShock3 rumble support.