HowTo bring the screen lock switch back to iPad iOS 4.2

In iPad OS 4.2 'Orientation Lock' was changed to 'Mute Switch'. If you want to change it back there is an app for that.

NoMute, a jailbreak only application, switches the controversial mute switch from iPad 4.2 into its former (and more useful) orientation lock. The plugin is free and you can get it from the BigBoss repository on Cydia.

By the way you can lock screen orientation without jailbreaking through multitasking panel - just push Home button twice, slide to the left and hit lock icon.