Tip: Create a new "test" user on your Mac
 

When trying software like OmniFocus there comes a point when you have live data in the application and testing how features work might start interfering with how your working copy is set up. In this case the thing to do is make a new user on your Mac and test the features there.

I've seen several people here mention that they create new users for testing, but I've talked to a few Mac users to who had never heard of doing it, so I thought it was worth a mention.

It's easy to do. Go to the System preferences, select Accounts, and click the + button. If the button is grey then you need to click the padlock and enter your admin password. Created a new user, call it "test" or "sandbox" or "george" or whatever, and leave the settings as standard, then click the Login options and turn on Fast user switching so that you get a users menu in the top right of the menu bar, making it easy to switch between your usual account and your sandbox.