I don't backup too often, mainly because in the moment I'm not doing too much stuff, that needs to be backuped. What I should consider doing is backing up a list of installed packages on my Linux system. Last time I had some trouble with some update made me almost reinstall my whole system. In the end I brought everything back to normal.
About RAID: RAID is not a backup solution. It's used either for data mirroring (faster access), or file restoration (if one of your harddrives gets corrupted), or both. A backup is completely independend and is used when your complete system gets corrupted.