Geohot has released his Limera1n jailbreak for iOS devices. Currently it is Windows only.
Remember if you require an unlock do not upgrade to iOS 4.1, you will need to wait for the next PwnageTool release. The only exception is the iPhone 4 which could be upgraded to iOS 4.1 without updating the baseband.
Details: ● iPhone 3GS, iPod Touch 3G, iPad, iPhone 4, iPod Touch 4G ● 3GS new bootrom is broken, fix pending ● 4.0-4.1 and beyond+++