Gottchas:

• Remember, putting you GPG keys on to your YubiKey is destructive operation if you save the state. Make sure to back up your private keys before putting the keys on your YubiKey.
• Backup up your YubiKeys on to a encrypted thumbdrive

Slides

References:

• YubiKey Guide - Great guide for putting your GPG private keys onto your YubiKey
• Ubuntu - U2FA PAM Support
• Ubuntu - Challange/Response PAM Support