Three comments: 1) USB sticks are not reliable as mid-term storage solution, neither are CDs/DVDs. USB sticks should only be used for transferring a copy from one location to another (temporary, short-term storage). 2) A RAID system with main drives is not an alternative to backing up data. Why? See, e.g., http://en.wikipedia.org/wiki/RAID#Data_backup 3) The paragraph about incremental and differential backup is not clear, not to say confusing.
On the safe side. A notebook without backup is like a car without seat belts. When unexpected problems arise there can be devastating damage. For that reason data backup should be as natural to us as fastening our seat belts. This article describes the various data backup alternatives, so you can know how to keep yourself out of harm's way.