While I love, love, simple and accessible learning material such as this - I really wish they'd encourage use of using a password alongside ssh keys. Seemingly the only draw to ssh keys for the layman is understandably disuse of passwords, but at that point (and perhaps accompanied by ill-set file permissions) you basically have your password to a remote machine written in a text file.
If anyone is learning something new in this article, please listen to me when I say when running `ssh-keygen` - put in a password. A simple one, I don't care. I promise you it's worth it.