I was using a quit smoking app called Quitter on my iPhone 4. It does not sync data to a server. There is no registration. Then I got the 4S and restored from backup. A couple of days later, today, I decided to check my quit smoking progress. The app was gone. Poof. So I fired up the App Store and re-downloaded it. I started up the app, and magically, my quitting data was all right there as if I never lost the app. How is this possible?