This is definitely a polished version of 3.1 Despite having to pawn and jailbreak it for unlocking it over a contract free iPhone3G, iPhone Dev team have done a wonderful job with Pwnage Tool 3.1.4.

The jailbreak is seamless and ultrasn0w continues to rock. The phone itself feels a lot more stable. Unfortunately, I am not sure what would be the result if you just restore the phone with the backup data. Being anal retentive, I continue to set up my phone as new every time an update is released.

But, I strongly recommend 3.1.2 and Pwnage Tool 3.1.4 for the jailbreakers and unlockers out there.