According to this story, Apple's "helpful" cloud storage service for music files wipes locally-stored non-Apple files from your disks, and replaces them with cheap sort-of-similar knock-offs that are only available when your network is up. I'm also hearing of other stories of people who signed up for this service, later cancelled, and found all their pre-signup music to be gone. This is the future of data storage?
In my case I use an old high-storage iPod with a large library of locally-stored music files for my car. I also frequently drive through areas with little or no network or cell phone coverage (Mendocino). We seem to be moving towards a world where making a setup like that isn't even possible: if all your data is on the net, then when you have no net you have no data.
Also, let this be a reminder: back up your files, and check that the backups contain what you think they should contain.
Carry on. :D