Here's a http://www.youtube.com/watch?v=PdrqdW4Miao The guy is wearing chain mail.
Thats a video, not an article detailing physics.
I surmise from the looks of it, though it is rather dark in there, that he is essentially in a Faraday cage.
I still hold that wearing a metal helmet in a thunderstorm is a very bad idea, no matter how much metal you otherwise are wearing.
Regardless, I do like the idea of armour being conductive to one type of magic, but resistant to another, and different types of armour having different strengths and weaknesses.
If its not in the vanilla game it would make a nice mod.
Though I think metal armour should increase the potency of shock spells, not reduce.