I've lost all my iPhone data by doing this:
* in iTunes, log out of the app store and back in with a different name.
* Plug my iPhone in and sync it.
* It wiped my entire iphone 3rd party apps because I was not the authorized user, as well as deleting my songs from my iPod, without warning me until after it was complete.
* I logged out of the iTunes store and back in with my normal account.
* I synced with the iPhone again. Everything was reinstalled, but without data.

If I had thought of it at the time, restoring from a backup might have helped but I didn't loose too much data myself (I'm not using anything like OmniFocus yet ).