The YouTube apps for Android and Google TV were updated today with functionality that allows you to share videos between the two devices. Google hasn’t fully entered Apple TV territory yet, but this is a start.
With this update, you’ll be able to begin watching a YouTube video on your smartphone or tablet and push it to your Google TV. When you do that, your mobile device becomes a remote control that provides you with basic functionality. You can also continue to use your device as normal while the video plays. Another neat feature lets more than one Android device to connect to Google TV at the same time. This could make for some collaborative viewing experiences.
Source [YouTube Blog]