Dunno how common this is going to be but,
If you are on iOS 7 and are doing a warranty swap your 'new' phone will be not be iOS7.
STOP. don't plug the thing into iTunes. it will automatically backup the blank phone and overwrite your backup.
just call apple support. there is a convoluted process to follow.
luckily I was able to recover an earlier backup, but according to the apple support guy, that was something of a fluke.
apparently there are some other wrinkles about apple ids being 'merged?' if you plug in anyone else's device.
Anyone have any tips. unfortunately I think i'm married to apple products for a while.