Official words from iPhone dev-team read:
We’ve released version 0.9.9b6 of redsn0w, with both a functional fix and cosmetic fix for iOS5 jailbreakers. For iPhone3GS owners with the 06.15 baseband, this redsn0w eliminates the network crash you saw when using Location Services in iOS5 (in fact, you don’t even need to disable Location Services anymore during the initial setup). The cosmetic fix is to the visual countdown you see when going into DFU mode.
It’s okay to re-run this redsn0w over an existing device jailbroken at iOS5. Just choose “Jailbreak” again and de-select Cydia (in other words, all the checkboxes will be unchecked). If you are lucky enough to have an old-bootrom iPhone3GS, please pre-select the IPSW first (redsn0w can’t yet auto-detect the FW version of your old-bootrom 3GS if it’s already been jailbroken)