It seems that the MobileSubstrates do not work properly on iOS 4.0.1 so if you are an iPhone 3GS owner I recommend you not to update to iOS 4.0.1 jailbroken because you may encounter problems trying to make decorations with ultrasn0w. MuscleNerd a announced that ultrasn0w does not work correctly with iOS 4.0.1 and the MobileSubstrate will have to be modified to solve this problem.
This warning is not applicable to iPhone 3G owners who can still use ultrasn0w on iOS 4.0.1. Jailbreak tutorial on iOS 4.0.1 for iPhone 3G you can find here.
