Let me ask you a few question: When you are working on a project (website, program …), are you working on that folder directly? Are you working directly on the files of the server? Are you working without constant backups?

If your answer is yes on at least one of these questions, I advise you to take a look at subversion (SVN). I’ll give a little resume on what this is but on Wikipedia the details are described in a great way.

What is SVN?

It s a version control system for source code, web pages and documentation and by using trunks, branches and tags you get a complete file backup system.
Before you start digging in to this kind of system, you need to understand the differences between trunk, branch and tags.

We are using tortoiseSVN to do all the SVN actions like committing, merging, tagging, exporting. It is based on Subversion and provides us a nice interface to work with this system. Off course, in Eclipse (the program we use to edit our programs and websites) subversion is integrated. (I think there is a subversion system for Dreamweaver on the market)
At any time you can go back to previously saved versions of your file. Isn’t that a super advantage and a must for everyone???

I recommend this system to everyone, it might cost you a little bit of time to get into it but it is necessary.