Apple recently released iOS 5.1.1 for Apple TV. It’s not a major update, and there’s nothing noticeable that comes with it. It’s likely just a few minor bug fixes.
The update is of course for 2nd and 3rd-gen Apple TV boxes, and to update you simply go to the devices Settings>Genera>Update Software.
Welp…not much else to add to that. Let’s just hope it fixes any potential issues you had with your Apple TV.