Hot on the heels of our annoucements of Xbox and Live Messenger integration (see "Instant Messenging Coming to the Xbox 360"), I found the little jewel to the left on Major Nelson's Blog in "Details of the next dash update".
Yes: it's a text input device integrated with an Xbox 360 controller.
You can read full details about the Messenger integration in "Instant Messaging comes to the Xbox 360". Looks to be available this coming summer.
From the post:
Current relationships on Windows Live Messenger and Xbox Live will be unified on Xbox 360 and users will see at a glance if their existing friends on Windows Live Messenger have gamertags, instantly expanding the breadth of connected experiences they can share online.
This means you can stalk and trash-talk your gamer friends like never before!