What is the Label property under the identity inspector in Xcode 4?

The Label field identifies the UI element in Xcode. If you name the UI element using the Label text field, you'll notice that element's name changes in the object list, which is to the left of the canvas.

The Label field doesn't do much with regard to code. It exists to make things more convenient in Xcode. In fact, the whole Identity section of the identity inspector exists to make things more convenient for you in Xcode. Suppose you have three text fields in your window. Giving each text field a different label makes it easier to identify each text field.