This is probably the second use that I started using Evernote for. If you are supporting a network of any size, you probably have some automated method in place to automatically back up the configuration of the various devices. Back when computer bulletin boards use to be King long before the Internet was invented by Al Gore, I had a hard drive fail and found out that you can never have enough backups of the data that is on the hard drive(s) that you have. I have carried that forward to keeping up with the configuration of everything on the network and as a side benefit, having version control so that you can see things change over time. Some devices, like the ASA, need to be backed up a little differently so that you can see some of the passwords/passphrases encrypted so that for the most part you can just about use the file to get a replacement device in service or replace the configuration with a known good version quickly. Some things, such as SNMPv3 user credentials, cant be backed up no matter how much you may try.
Keeping track of the all the different configurations and versions for all the devices can be a little overwhelming. I use a combination of Stacks and Notebooks to keep all of the configurations organized. While some may say that the system you have in place is all you need for this but there are times that you may not be able to get access to the system where the configuration files are kept. By being able to have it with you may just be the one thing that will help you get a problem resolved or get a piece of gear up and running a little faster. I setup a notebook for each device and use the Stack function to organize the devices by either location or type of gear, whatever works best in your situation.
Now that you have built a foundation of making another copy of your configurations, use this as a step to the next level. Between the periodic backups, I also use this to plan configuration changes to equipment as well. This helps me make sure that I dont miss out on anything and helps build a knowledge base of how I did something in the past, so I can maintain consistency or see how I can do something better as the opportunity presents itself. By using the shared notebook functionality, you can have what you are doing being shared with others in your group so that everyone can benefit from what everyone else is learning and doing. Everybody wins in this type of situation since you can build on what others have done and not have everyone learning the same things on their own.