I’ve been using Dropbox, Carbon Copy Cloner, iCloud, iTunes Match, Time Machine, Google Drive and Crashplan as part of my back up plan for a while. Recently I also added OneDrive and Copy, because they both give me a decent amount of cloud storage, and in the case of Copy it’s a decent interface to store large PDF files (such as downloads of Mac Format and Linux Format) that are too large for the Kindle app to deal with.
Today I also started experimenting with BitTorrent Sync. It’s not cloud storage, but it will mirror directories between multiple computers, and is only limited by disk space and the speed of my local network. I’ve not got much further than installing the client yet, but will write more about how it works if it proves to be interesting/useful.