The only time you need to "re" jailbreak your phone, is if/when you update it through iTunes when they release a new software upgrade. When you update through iTunes it wipes out the old firmware, and installs the new. It's kind of like reformatting the drive your PC, thus erasing the jailbreak. After it does that, it reconfigures your phone from the back up it created prior to the update as far as your settings, apps, ect. They will create new jailbreak software, if they need to, after Apple releases a new firmware upgrade. I say "if they need to", because, the jailbreak for firmware version 3.0, worked as well for the version 3.0.1 . It depends on how and what is changed in the software. With all that is being changed and added with 3.1, a new jailbreak will have to be created. I'm sure others could explain it better and more accurate. HTH.