I use JungleDisk (https://www.jungledisk.com/ https://www.jungledisk.com/) - it's good because it can be used for backups, syncing, and previous versions of syn

I use JungleDisk (https://www.jungledisk.com/ https://www.jungledisk.com/) - it's good because it can be used for backups, syncing, and previous versions of synced folders. It also does multiple users and multiple operating systems (Mac/Windows - probably does Linux too but I haven't checked). It's also quite cheap. I previously used Mozy, which was excellent, but only does backup. Mozy was much more efficient over the wire, better at notifications and better about resuming very large backup sets. But unfortunately doesn't do synced folders and the rest.