I have one at work, and another at my parent's house, more than 100 miles away. In case of a literal blaze and/or high water, even the local drive should be fine. If all drives are gone from a single catastrophe, I figure I (and everyone else) have more serious things to worry about, like what's for dinner.
How often can you swap them?
https://secure.backblaze.com/user_signin.htm type your username, password, and click "Sign In", then....
Look on the left nave for "View/Restore Files", browse to one file you know you changed recently, and check the checkbox by it (and maybe a few other files) and click "Continue With Restore". Done!
Within a few seconds you can go to "My Restores" (on the left side of the web browser) to download the restore!