Nice little secret perk for ya.
Alright so firstly you need to have gotten far enough in the main quest to be able to recruit followers for the Blades (in Sky Haven Temple) from there you must recruit three followers into the blades. Then talk to Esbern and complete the Dragon Hunting quest, when you kill the dragon keep atleast one dragonbone and one dragonscale, return to Esbern. He will now ask you to help him with his research agree and you need to give him 1 dragonbone and 1 dragonscale.
In return he gives you a potion that once drunk gives you the secret perk, Dragon Infusion. This perk gives you a permanent effect of 25% Less Melee damage from Dragons.
Added by: nightmare2 Jun 30th 2012, ID#4723