I'm not sure how restoring an app from a back up would be better than re-installing an app from Zune unless you are talking about saved games or something. But I'm not aware of anything that backs up that kind of data.
All different types of tracking apps. Finance, gas MPG, calorie counting, stuff like that. I have a couple years of MPG tracking that I obviously know will not transfer to my WP, but if I got a 4S everything seamlessly transfers from the backup.