Today Microsoft annouced a new technology to use with the Xbox called SmartGlass.
“SmartGlass brings AirPlay-style wireless technology to Xbox and Windows 8 by letting you send video from your tablet or phone to your TV. It then turns that second screen into an information window giving you data of the content you’re watching. Plus, it updates the info on your mobile device as the content on the TV changes.”
We will have to wait and see what options will be available for computer and mobile device screen sharing to and from an Xbox.