Apple released 5.1 update today for Apple TV 3rd and 2nd generation and you can download it anytime. You can go to setting menu, general and then select for update software.
This new update is included Shared Photo Streams, AirPlay, iTunes account switching, Trailers, Screen savers, Main menu, Subtitles, Network configuration, Stability and performance. We are checking on Subtitles from update to see what does it help to improve on Apple TV and we will let you know soon. =)