Tell me how you backup your sites

When you backup the files on the server to your home computer, how do you organize those files?

Lets say you have a drive on your computer dedicated to just website stuff, with a folder for each site,,,, but then what? Do you make a folder for every month you backup your sites, would you label the month and day?

What if your running a content management system, how do you store your themes, plugins,,,, modifications.

The problem I'am having is organizing all of my backup files so their easy to find. I have a folder for wordpress, with every recent version under it, then the modifications.

Then there are the vbulletin files for my forum. I download a lot of mods, look at them, then I may or may not install them. So I have tons of themes, and modifications that I might want to hang on to, but their just taking up room.

Lets take a wordpress theme for example - I might edit it one way for one site, and another way for another site - so that leaves me with 3 versions of the same theme: The original, site A and site B.