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, don’t 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 don’t bug us about this).
    • Any information we have regarding this update will be posted here.
    • You can also follow us on twitter - @iphone_dev