Ubuntu-One is an excellent tool to synchronise files and folders between multiple machines using the "ubuntu" cloud as storage. Synchronisation is done automatically when it detects a file change.

However, Deja-Dup is another versatile tool in that you can backup & restore folders to local storage, a local network machine, a remote machine or indeed to a Rackspace or Amazon Cloud - and can be done on a timed-schedule.

I use both Ubuntu-One and Deja-Dup to provide backups - Ubuntu-One to allow me to sync files across multiple computers in real-time and Deja-Dup to backup Ubuntu-One files on a timed-schedule.

The reason I do this is the small-print in the Ubuntu-One terms & conditions - you are responsible for backups of files in the UbuntuOne Cloud.