Both the Xbox and the Playstation have come out with their own controller based keyboards. These keyboards are implemented to make sending text based messages easier. This has a little bit more of a function on the Xbox seeing as they have MSN integrated in to it.
The two consoles have gone for very different designs. Well no, thats not true, the only difference is where they put it. Just as history has displayed the two competeing juggernauts will NEVER blatantly copy one another. No no, they will just ALMOST copy each other and make one big cosmetic difference ( black console, white console) and act as though it's an idea all their own.
Here are the two:

The Xbox 360: In our opinion better placed for optimal thumb movements. The keys are soft and push in but don't click. They have a rubber feeling and are spread apart far enough that it's not too difficult to hit each key (the key word there is "too").
The PS3: Pretty much an exact duplicate of the Xbox, is on top instead of the bottom of the controller. The other difference is the replacement of some fundamental buttons. By this I mean Sony created a plate used to attached the Keyboard (the Xbox does not have this, which is a benefit) and this plate covers some key buttons (home button, start, select). To make up for this they have a Wii like idea where they just placed buttons on the plate which push the ones below it.
All in all we have to give it to the XBOX. They had theirs released some time ago and it's more comfortable. Also we found that having MSN on Xbox Live was a good purpose for the accessory.