Apple released iOS 4.2 GM for developers that you can download from the developers area on the Apple website. This is the last version before iOS 4.2 will be released for public. There is said to be 100+ new features and innovations included with this update.

There is one thing changed that not everybody will like, the screen lock rotation switch has now been repurposed to act as the mute button.

Also Apple has changed the multitasking bar, it has been expanded to include more features such as the new AirPlay button.

Source [modmyi]