iTunes <-> iPhone. At sync time, a back-up is performed. Which data is included, which data is not? i.e. are songs (potentially redundant) backed-up so that a computer ends up having both the source file on the filesystem and the copy within the device back-up? Is anything on the iPhone filesystem not backed up? (i.e. on a Mac using Time Machine, some files are excluded from the back-up even if not all of them can be recreated upon restore - I lost my postfix config this way..)