iOS 4.0.1 for iPhone was released a few hours ago and those of you who have an iPhone 3G are already able to update and jailbreak iOS 4.0.1 using RedSn0w 0.9.5b5-5. Note that RedSn0w will jailbreak the iPhone 3G only. At this time, there is no jailbreak for other devices on iOS 4.0.1, which is why you should not update if you rely on your jailbreak.
Instructions to jailbreak your iPhone iOS 4.0.1 with RedSn0w remain the same except you must update to iOS 4.0.1 and point RedSn0w at the 4.0 IPSW even though you’re at 4.0.1.
Stay tuned for more info!