You know, on the iPod, if after filling it with songs, you go to the computer in which the songs are backed-up, and delete them to free up some space, and then change the auto-update feature on iTunes, all the songs on the iPod disappear without warning.
Apple may be “easy-to-use” and this aspect appeals to a lot of users, coupled with the delibrate hiding of advanced settings, but there are some aspects of it that will drive one mad. Processes that don’t ask for user confirmations, for instance. For others that annoying box that Windows keeps popping up for every tiny system change, is appreciable.
Funny, I’ve done exactly that and my iPod didn’t auto-delete all the songs on it.
By the way, iTunes *does* ask you if you are sure on major decisions like deleting files. If you check the box that says “don’t ask me this again” it doesn’t (unlike MS). My guess? You checked the box and don’t remember doing it.

I'd say that that's enough warning.
Back up your ITunes library (and anything else important) to an external hard drive. They're cheap.