Here's a thought, why not back up your entire HD?
Bad idea.
First of all, if you should ever need that backup, you would have to know where's the useful data that you want to restore. Now think about this for a second: is it easier to find the right stuff at the moment you back it up or after weeks/months/years of storing it somewhere? It's a no-brainer, so only backup useful stuff then you can really use your backup archive when you need to.
Second, not many of us have unlimited backup storage. If you need to back up -say- half a terabyte every month, you will need 3TB storage for half year's backups. Granted, not many of us want to keep that many backups, but still, you get the picture. If you backup 100%, then you need 100% extra storage for one backup. If you backup 25%, then 50% extra storage is enough for two backups. This is more like a theoretical point, but still very valid. Storage space is not that expensive, but how much is too much?
Lastly, mark my words: "you will need backup archive some day". The day will come, even if everything has been reliable so far. And when that day comes, you need to have a *usable* backup that is also up-to-date. If you only have a year-old DVD that has been scratched to be unusable, can you really call it a backup? No, it's only useless piece of plastic. Or if your backup is scattered to multiple locations and you won't find what you're looking for, then is your data safe? No. Unless you manage to restore lost data, your backup is worthless.
There's also an old saying worth mentioning: "nothing is backed up until it's backed up twice". Trust that. And if you also want to make your life easier for the moment the disaster strikes, please do yourself a favor and *think* ahead about what you're backing up. To repeat myself; think about what data you absolutely want to be able to restore!