It's been quite a while since Apple released the OS 3.1 for iPhone and there's been a lot of confusion regarding it's Jailbreak Status etc. Therefore, here's a summary of do's and dont's
According to ChronicDev, that the 3.1 GM seed is still vulnerable.
It has been confirmed by MuscleNerd from DevTeam that iTunes 9 doesn't interfere with jailbreaking so you can update iTunes but make sure that you do not update your device firmware to 3.1 yet if you want to jailbreak.
Saurik confirms once you update to 3.1, there's no way to downgrade to an earlier version as iTunes no longer signs the older firmware. Therefore, if you do not have your ECID information saved, you're completely stuck! For those who have the information saved, there should be a solution out soon
The new firmware also includes a new baseband which means none of the current unlocking tools