When I did an upgraded from 3GS to iPhone 4, I did a restore and after a week the phone crashed. The phone didnt want to turn on, plus I did not do a backup and all photose went bye bye. Went to apple genius, he said and suggested when upgrading to a newer model you better want to start fresh, since the device might have different hardware/software connections that are in the backup files.
Seems strange to me, but after that accident, every time I do a phone upgrade I start fresh.
Hope this helps!