iPhone Dev Team has released Pwnage Tool 4.2. It incorporates the new kernel based exploit of GreenPois0n for creating full untethered iOS 4.2.1 custom firmware files. PwnageTool supports all 4.2.1 devices except iPod Touch 2G.
List of iDevices supported by Pwnage Tool
• iPod touch 3G
• iPod touch 4G
• AppleTV 2G
iBooks and Wi-Fi problem on AppleTV 2G fixes would be available in upcoming Cydia package updates. So if you have already jailbroken your devices, we advice you to wait for these updates rather than restore and jailbreak again.