I always found that studying Office Actions and their responses by other patent practitioners is a great way to learn. This week I looked through the prosecution history of US Design Patent D650355 to Apple. It covers the Design of an iPod, and was coincidentally posthumously awarded to Steve Jobs.
The application was subject to several rejections. In response to the Office Action the Applicants pointed out the differences between the prior art and the claimed design – which convinced the Examiner. Good reference to keep in mind if you have to argue an obviousness rejection in a design patent app.