The 3.1.3 firmware update for the iPhone is out now, available through an iTunes update. It's no revelation, fixing only the accuracy of the 3GS battery meter and the stability of some third-party app launches. It appears that iPhone 3.1.3 closes the usb_control_msg exploit, used by blackra1n. Therefore you should NOT update until after it has been fully jail-broken. If you have mistaken upgraded to 3.1.3, you can follow this guide to downgrade back.