I've been using Subversion for a while now and I love it. It does what it says on the tin reliably and efficiently. I've also used it in conjunction with ISO9001 change procedures, and here are some things you need to know:

1. Subversion is not a documentation control system, it's a file control system. You need something else to handle ECNs.

2. As you work with your source files (Electronic CAD, FPGA, C source, whatever) Subversion is the best way to handle your working revisions. You can commit changes anytime you have made a change that you want to keep.

3. Somewhere along the line you will want to issue your files to production. This is where an ISO9001 quality system kicks in, and you need an ECN process to make sure changes are suitably approved and controlled.

4. When files that are revision controlled by subversion are issued you only really need to record their subversion revision to have a full record as you can always get files of that revision. In practice it is a good idea to take a snapshot of the files and put them in a 'current production' data folder. Asking all users to check out a specific revision when they want production data is too risky.

5. There are quite a few client programs and personally I recommend TortoiseSVN. I also use a command line client, and I know there is a client dedicated to Microsoft Visual Studio.

6. You can use the command line client to check out a specific revision at the start of a build process.

7. You can also use the command line client to update the revision and embed it in source code. This closes the loop as you can then inspect any build to find the source revision.

8. An important role for the administrator is to choose the authentication scheme and the checkout and commit permissions for the different users. The SVN handbook is a very good reference on this topic.

9. Training is very important. Subversion is easy to use, but the whole concept of file revision control is more complicated. Users need training and practice to get the hang of when to commit.

Once you've got the hang of file revision control you will never want to work without it. Knowing that you can roll back if you've made a mistake is a real boost to productivity.