It's not only the iPhone DevTeam who are busy these days updating their apps to the latest iPhone 3GS, Saurik has also released a new version of MobileSubstrate and WinterBoard. This two great apps that can enable many different add-ons and themes for the iPhone is now 3GS compatible.
Saurik announces the great news via his Twitter account:
The newly released 0.9.2958 versions of MobileSubstrate and WinterBoard (upgraded to support ARM7/Thumb2) should now work on the iPhone 3GS. If Cydia asks you to upgrade WinterBoard, you should. Regardless, you can read the changelog: I fixed a few 3.x bugs. ;P