But then again you'll never know. Wireless syncing and even background syncing is bound to come.
Well, actually, we already have wireless syncing of selected information, with MobileMe.
Background backups (as opposed to sync) are problematical. You can backup an app while it is in use, but not it's data. You really want to back-up the data while the app is not running. Otherwise, you are potentially getting an inconsistent snapshot of it's data.
Sync/backup is a complicated mess that most users will never understand. Some stuff syncs to a directory, some syncs to a "cloud", some is just backed-up (as opposed to 2-way sync) and it's keep in several different locations. (The "backup" is just app data files and a few system-wide data files. Apps are kept in an iTunes directory, and not specific to a particular device. Music, of course, is synced to iTunes. Pictures are synced either to a directory tree or iPhoto...) The 'backup' is under Library/Application Support/MobileSync, but is not a complete bundle of "everything" on your device. The backup is "de-duplicated" in this way, but it makes it hard for the user to understand.
If you want to "backup your backup", you'd have to have considerable technical knowledge to know what to backup. Of course, you should be backing-up your Mac's home directory (assume you have a Mac) and that WILL catch everything. But many people will exempt iTunes from frequent backups, choosing to back it up separately (less frequently) or not at all because it can be very large. This would lead in incoherent device backups.
