limera1n has been released.
It works with iOS 4.0.x and 4.1, and supports the iPhone 3GS (old and new bootrom), iPod Touch 3G, iPad, iPhone 4, and new iPod Touch 4G.
I have a new bootrom 3GS, and it was really easy to jailbreak. I just ran limera1n, pushed the button, and followed the on-screen instructions.
I may post more information here: https://xenomorph.net/apple/iphone/jailbreak/