The iPhone Dev Team has released RedSn0w 0.9.15b2, which fixes a few items for owners of older devices.
The most outstanding fix is for 3GS owners with old bootroms — RedSn0w 0.9.15b2 brings back untethered jailbreak support for end users who fall into that category.
Most of the changes don't pertain to owners of newer devices, but it's always a good idea to ensure that you're running the latest and greatest version anyway. Take a look inside for the full release notes.