updated 05:37 pm EDT, Mon May 7, 2012
New iPad, iPad 2, iPhone 4S still unsupported
Third-party jailbreaking utility redsn0w has been updated for iOS 5.1.1, which was released by Apple just earlier today. Currently the hack works only in tethered mode, meaning that a device has to be connected to computer anytime it's restarted. It's also restricted to devices based on A4 processors, excluding the third-generation iPad, the iPad 2, and the iPhone 4S.
The rapid turnaround is possible because of a long-known exploit related to the A4. A5 processors have proven more difficult to crack, such that a recent untethered iOS 5.1 jailbreak still lacks support. The v5.1.1 firmware could potentially further set back jailbreak attempts, although as a maintenance update there are fewer changes than were present in v5.1.