You can already jailbreak your iPhone and iPad, and that's common knowledge. But now, you can also jailbreak your Apple TV too. The first untethered jailbreak for the new Apple TV software (5.0.1) is thanks to Seas0nPass.
According to Seas0nPass, you can add these plugins to your Apple TV:
Couch Surfer Last.fm Maintenance Media Player NitoTV Plex RSS Feeds Rowmote Weather XBMC