Don't try and do it yourself. You should be using a program such as amanda or bacula to manage your backups.
Use amanda when you don't have a tape library.
Use bacula when you have a tape library available.
mini rant follows
Sure, just using
tar works and is simple.
How easy is it to restore a certain file from a week ago? A month ago? How do you keep track of what's where? Remember, backups are easy, but restores are the important part.
You can design a method to keep track of what's going on and do all that work yourself. Go ahead! Enjoy the pain when things get complicated. But what you gain from taking the short amount of time out of your schedule to configure amanda (okay, it's more for bacula, but it's more complex. Bigger investment, bigger setup, bigger return) you get back almost immediately. We use it for even single-server backup scenarios as it's so easy to set up and you gain what you spent many times over in the long run.