Shake to undo:
When you are typing in Mail, Safari, Notes or Messages, and have messed something up – just shake your iPhone/iPad. An alert will pop up asking whether you want to Undo Typing, or remove what you have just entered. If you do it and then change your mind, don’t worry – just shake the phone again and you get the option to Redo Typing to bring it back again. A simple but very useful tip!
Here is a best buy video demonstrating the functionality: