Was taught to develop a good backup strategy when I designed my file structure. The most important part of your system is data. Without good data everything else is worthless.
1. Complete System backup done at system baseline and incremental backup after every configuration (application install or remove) change stored on external HD or different machine.
2. Complete Data backup. All data that changes is on one directory branch to an external HD.
3. Immediate backup of all critical data, e.g. Quiken, Time & Chaos, Serial number and Passwords after every use by emailing them to a web mail address for free off site storage. Also is included in data backup.
This way i can get access to my critical data 24/7 from any PC and for a System restore (if it was a HD failure) is New HD->Complete System restore->all Data files (containing critical data) gives me an up to date system quick and simple.
For example there are actually 4 copies of my checkbook. First is original, 2nd is backup done by the program itself to the Data branch, 3rd is my external drive and the 4th in my mailbox.
Using PGP & email I have a reliable, secure and inexpensive backup solution.