Previewed at WWDC, launching in the fall.
iPad OS 4.2 'Orientation Lock' to 'Mute Switch' Change Permanent
One of the controversial changes in the upcoming iPad OS 4.2 was the change in functionality of the iPad's Orientation locking switch to a Mute switch.
...the physical switch on the iPad's side for locking the screen orientation has been repurposed as a mute switch. The change has been confirmed by posters in our forums.
With the change, screen orientation locking is now accomplished within the multitasking tray as on the iPhone under iOS 4.
Q: In IOS 4.2 for iPad is the switch on the side going to be the mute and not screen orientation lock from now on?
Steve Jobs: Yep.
Q: Are you planning to make that a changeable option?
Steve Jobs: Nope.