2nd-generation Apple TV owners will be happy to learn that they can now jailbreak untethered, thanks to GreenPois0n RC6. This is a huge improvement over the previous jailbreak, which required that the settop box to be plugged into a computer when rebooted.
This jailbreak installs NitoTV on your device. This means that you will no longer have to load said software through the terminal, a much, much more convenient solution to users.
For now, be cautioned that the jailbreak is actually still in its beta stages. There are reports of minor issues such as wifi problems and booting. Of course a device like Apple TV 2nd-gen can't do much if not connected to a network, so proceed with caution if you choose to run the jailbreak.