From my understanding, Apple doesn't let you ship desktops for repair anymore. I inquired about this when my friend's iMac was having problems. He lives about 70 miles from the nearest Apple Store or Apple Authorized Service Provider. The AppleCare rep said that they will only send you a box for a notebook.
On the other hand, if you have the AppleCare Protection Plan, a desktop usually becomes eligible for on-site service.