The version we were able to demo was still a prototype, but was close to the final version that will be released. As for the physical characteristics, the Chatpad was extremely light, but did not feel flimsy or breakable. The keyboard layout is well done and will work for anyone regardless of hand size. Despite not being able to actually use in game (although I tested it inserting some text into the profile page), the responsiveness of the keys was very good, and the final version will have LED backlighting.
As for the connectivity, the Chatpad fit well onto the Xbox 360 Wireless controller to the point that I believe most gamers will simply leave it on instead of constantly swapping it out. The impact to the weight and balance of the controller was negligible, and besides your pinkies not being able to wrap under the grip of the controller, you wouldn't even know it was there IMO.
No cost or street date have been announced yet, but my guess it will be attractively priced (possibly bundled) so that most users will pick it up without a second thought. I know it will be a must have for me.