I had no idea that YubiKeys could store SSH and GPG keys. Currently, my whole digital identity can be trivially bootstrapped from my SSH key and my GPG key:
It would be really nice to back these with a hardware store.
They only store gpg keys (as a smartcard), but the gpg-agent tool can use gpg keys for ssh (as a drop in replacement for the ssh-agent tool).
You can use gpg-agent to use any gpg key as an ssh key, not just a smartcard one.
A great guide to setting up GPG and ssh with a Yubikey can be found here. I found it very helpful.
Ah, understood. Very cool!
You may also want to look at pivy which allows SSH key and other signing use of Yubikeys and smart cards without the GPG business!