The iPhone dev team released the latest version of its PwnageTool for iOS 4.3.1.



From TUAW:

Thanks to the work of Stefan Esser, both the PwnageTool and redsn0w now provide an untethered jailbreak for this latest version of iOS. This untethered jailbreak is compatible with all 4.3.1 devices except for the iPad 2 which is not susceptible to either the limera1n or SHAtter bootrom exploits.

  iOS 4.3.1 jailbreak available, but not for iPad 2