I've been nagged to update an iPod to iOS 5 for weeks now. Since it's not mine, I want to be as careful as I can. I'll follow the procedure exactly as Apple recommends, and the device has never been jailbroken. For all intents and purposes, a normal iPod.
However, I'd like to inform this person of all the possible risks that this could have. Since I've never done this upgrade before, I have no idea how it'll go.
So, my question to you: What could happen and what is the likelihood that it will?
(I don't need impossible-to-find statistics, though they might be helpful; I'd just like something like 'Oh yeah, I updated 150 devices and 3 were xyz')
BTW, this is the second-latest iPod and it currently has iOS 4.latest.