You should always perform the final phase of debugging on the device. Simulator does not perfectly simulate the device. For example, you must use the mouse pointer instead of finger touches, and so manipulations of the interface requiring multiple fingers are not possible. In addition, Simulator does not use versions of the OpenGL framework that are specific to iOS, and it uses the Mac OS X versions of the Foundation, Core Foundation, and CFNetwork frameworks, as well as the Mac OS X version of libSystem.
