The Firmware build is 8C134 and finally unifies the iOS of the iPhone, iPad, and iPod Touch. iOS 4.2 also brings multitasking and other 4.0 features to the iPad. Hopefully, iOS 4.2 will be released soon and include a fix for the daylight savings bug.
iOS 4.2 also offers new features such as AirPrint and AirPlay.
AirPrint automatically finds printers on local networks and can print text, photos and graphics to them wirelessly over Wi-Fi without the need to install drivers or download software. HPs existing and upcoming ePrint enabled printers will be the first to support printing direct from iOS devices.
AirPlay lets you stream media from your iPhone, iPad, and iPod touch. So if you feel like watching a movie you have on one of your devices, you dont need to rent or buy it again. Just tap to start playing content on your iPhone, iPad, or iPod touch, then tap again to instantly stream whatever youre watching or listening to directly to Apple TV.
MacStories has already installed the new firmware and confirms that AirPlay is indeed working for the official YouTube app. They also note nice system-wide AirPlay controls in the multitasking tray and redesigned button and volume / brightness controls.