Kotaku: The Wireless Keypad for the Playstation 3 is an innocuous little snap-on peripheral, that adds a full QWERTY thumb board, touchpad and a few instant access buttons to your controller.
The Playstation 3's $50 keyboard is a bit lighter, thinner and offers a few more features than its Xbox 360 counter-part, which is to be expected since its hitting stores so much later.
Is it worth a purchase? Sure, if texting with a controller drives you nuts. Otherwise I'd maybe hold off until I felt a need for a keypad on the controller.