Thanks to forum member iPhonephreak for giving heads up to NOT update the just released 3.1.3 FW.
Here's what the Dev Team have to say from their webpage:
WARNING! At 10.30AM PST on February 2nd 2010 Apple released the 3.1.3 version (7E18) of the iPhoneOS.
If you care about your jailbreak and unlock, donít update your device - 3G and 3G(S) owners should pay particular attention to this warning.
- PwnageTool and redsn0w are not yet compatible with 3.1.3
- There is no estimated release time for compatible tools (please donít bug us about this).
- Any information we have regarding this update will be posted here.
- You can also follow us on twitter - @iphone_dev