iOS 4.1, which was announced last week, is now available for download via iTunes 10. And, in mere hours, iOS jailbreak developer pod2g announced on Twitter that it has been jailbroken. This, it turns out, is far more serious an exploit than previous jailbreaks, as it takes advantage of the boot ROM of iOS devices. There's still some work to be done on the exploit, but once completed Apple is unlikely to able to plug the gap without some hardware changes.
As for the update itself, it delivers a number of bug fixes and new features, the former of which include notably improved performance on the iPhone 3G, and a fix for the reported proximity sensor issues. New features include: Apple's much-touted HDR photo mode for improved dynamic range in photos; the ability to upload HD videos via Wi-Fi (iPhone 4 only); TV show rentals directly to iOS 4 devices; and Ping integration into iTunes.
All these updates, and more, are available now, and the full jailbreak is no doubt in development as well.