iPhone3GS owners in our comments section below noticed a problem with the untethered jailbreak available for the old-bootrom 3GS. We’ve corrected that problem in 0.9.9b9d. If you have an old-bootrom 3GS and have already used last night’s redsn0w on it, you can re-run it again without losing anything. Just use this new version, go to Extras->IPSW and manually select the 5.0.1 IPSW, then go back and Jailbreak it again (but you can uncheck Cydia because it’s already installed).
Keep in mind this jailbreak is still tethered unless you have an iPhone 3GS with the old bootrom. You can grab the updated version via the links below then check out our guide on how to jailbreak iOS 5.0.1 via redsn0w. If you have questions or run into issues, check out our jailbreak and unlock forums as well!